Judging by the fact that Episode 7 was a 'new take' (not so much) of A New Hope, I'll go with the "Episode 8 will be Empire Strikes Back 2.0" bandwagon, since it seems to be the safest bet for speculation.
Now, going by what we have in this teaser (can't wait for the real trailer) I'll go with some wild guesses:
* POTENTIAL FORCE AWAKENS SPOILERS BELOW *
1) Now, obviously, Luke trains Rey, predictable since we saw Force Awakens.
2) However, I don't think that Luke will just generously do that from the start (figuratively speaking... it'll still happen soon in the movie since you have to tell the whole story in less than 3 hours, more like 2 hours and some minutes). From the beginning Luke will most likely refuse, or very heavily go against the very idea that anyone else in this entire galaxy should have to get through the whole mess of what it really means and really is to 'become a Jedi'. At the end of the teaser, what Luke says I think actually happens (that scene) fairly soon in the movie perhaps even before Luke starts to train Rey. It's going to be part of his initial mindset that, in his views, it's essentially time for 'The Jedi' to end. He's been through enough, including what we haven't seen on-screen but was briefly explained in Awakens (I.E. that Luke 'lost' the Jedi Order, that he 'failed' the Jedi, or 'failed' being a Jedi enough to see that mess coming... and of course that he failed Ren).
So basically, skipping a lot of thoughts on that but he's going to have the initial "Never gonna happen again" mindset, and has a conversation with Rey when he stops, turns around to look towards Rey and replies with that line in the teaser. Oh and... that's of course IF that scene even makes it in the movie, because there's been a trend since the past couple of years where they show teasers in which there's one or more scenes that in fact do not end up in the movie, which actually happened with Force Awakens... and more on that below. But, after some time, perhaps Rey manages to talk some sense into him and convinces him that she needs training, and that ultimately it's really not up for discussion as long as Luke lives. And he will oblige, but without a smile on his face.
3) Now, just like in Empire Strikes Back, screen time for Rey will be focused on her for a large part of the movie while she stays on that island being trained by Luke. We'll have occasional scenes where we "go back" to them to see her training progress (or not much... we'll see).
4) I'm seeing that one coming from LIGHT YEARS away, but as Rey will be trained she will eventually have to meditate with the Force. Just like Luke experienced, Rey will have visions of a future that - just like Luke will surely tell her as much as Yoda told Luke - is always in motion and cannot be relied on for accurate predictions. However, real bad things will happen to the Resistance, and to Rey's friends. She'll feel that the urgency gets on her personal side, affecting the only group of people she cares for (well, her friends), and she will brashly want to interrupt the training to go help them. So... yeah... Luke will be against it, will warn her that she's not ready for that stuff yet, but she'll say something along the lines of "But I have no choice! I MUST go help my friends!" (it's gonna be cheesy but it's the gist of it).
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Now, there's interesting things to further cement my impression that The Last Jedi is, indeed, gonna be Empire Strikes Back 2.0:
º Obvious nod (at least, if not an essential repeat of the Battle of Hoth) at Empire Strikes Back with that shot of those Resistance (most likely) fighter-type ships flying towards a row of what looked like the new First Order's AT-ATs on the horizon. Those ships will almost guaranteed be a new take on the Snowspeeders of the Battle of Hoth. Their weird design leads me to believe that they'll probably have some sort of a 'cable' that they'll have to attach to those AT-ATs while circling around them to bring them down. I KNOW that they're just going to do that AGAIN... but wait, the ships have a different design so it's gonna be easier to digest. Anyway... as I said... just my wild guesses but I don't think that The Last Jedi is going to innovate on many aspects for Star Wars in general. I only demand to be proven wrong but I'll only know that for sure in December. In the meantime I'll just go ahead and prejudge The Last Jedi as merely Empire Strikes Back for the new (younger) generation.
º Now I mentioned earlier that there seems to be some sort of a trend (be it intentional or not... I don't know, so I'm just using that word to describe this 'phenomenon', for lack of other ways to perceive it) since a couple of years with teasers - and sometimes whole trailers even months after a teaser was released - in which one or more scenes are shown but do NOT end up in the actual movie. Now, that actually happened with the Force Awakens trailers. There's a scene where we see Luke in his Jedi attire placing his cybernetic hand on R2-D2's head in a location that seemingly had seen some battle, it's partly on fire around them and it looked like they got there after said battle occurred only to be the witness of the destruction. That scene Does. Not. Exist. In. The. Movie. And on a side note it's not the only trailer scene that didn't end up in the movie. There's also that shot during a night time storm if I recall correctly, with Kylo Ren with his ignited lightsaber and his "Knights" around him.
But, with this said, I've noticed something interesting in this Last Jedi teaser. The scene where at the bottom of the screen we're seeing Luke, yet again accompanied by R2-D2, to a location that HEAVILY hints at the EXACT same non-existent scene from the Force Awakens' trailers. I'd go as far as saying that the scene in question is basically now complete for The Last Jedi but was probably originally designed or even partially shot during the filming of Force Awakens (but for some reasons just never included in that one). The location in question seems to be the (then-new?) Jedi Order's Temple in ruins and on fire. I THINK that it's going to be a flashback scene for either Luke himself or possibly for Rey to witness through meditation with the Force. A scene that will show us what actually happened (in part) when Ren attacked the Jedi Order back when Luke was in charge and trained Force Sensitives around for a living after Return of the Jedi.
Now, everyone, keep in mind that the scene in question in this new teaser might - once more - end up being removed from the final cut. I hope not, but it could happen. If they do remove the scene then I only hope that Luke WILL describe a bit more of what happened via dialogue with Rey during (or probably before) her training starts.
º The context for both the First Order and the Resistance in The Last Jedi is very similar (heck, almost identical) to how the whole situation was for the Empire and the Rebel Alliance back in Empire Strikes Back. In The Last Jedi, the First Order don't have their precious sacred Death Star 3.0 anymore, but they did wipe out the Resistance 'HQ' before going down (Hosnian Prime? The New Republic capital and 'home world', along with the majority of their fleet stationed there... along with the rest of that planetary system basically). In Empire Strikes Back, the Empire had just lost their DS, and decided to build a new one (very good plan by way... very... very good plan). So yes, I call it now, the First Order will most likely repeat the Empires' mistakes and will create yet again some sort of a new "superweapon" to replace their Starkiller base (I only hope that it won't be a giant sphere again). In the Last Jedi, the Resistance don't have their 'homeworld' anymore, just as in Empire Strikes Back the the Rebel Alliance lost their Hoth base (and their 'grip' on that system). Now, obviously, losing a whole plantery system along with a whole planet that happened to be the HQ for the New Republic is sort of a MAJOR BLOW that's on a completely different level than the Rebel's situation back during Empire... but still... during Empire the Rebels weren't exactly able to take on the entirety of the Imperial forces even in their best dreams.
So the gist of all this point is to say that the Resistance (big surprise) will be... * drum rolls * ... on the run. The battle we're seeing in the teaser, as previously speculated, will be a replacement for the Battle of Hoth. Which means that they'll have to get the hell out of there ASAP (that's what Po tries to do and ends up stopping short of being blow up with that X-Wing in the hangar). What I think is going to happen is that the First Order is after Fin and surely other stuff (intelligence-related, plans, anything that the Resistance hides there, etc), but Fin is still in artificial coma or something, healing from his wounds in Force Awakens. So Po tries to take Fin's "pod" of healing magic away from the base while the attack occurs on the surface. The new Snowspeeders will do their Merry-Go-Round maneuvers and heroically die trying while some of them manage to get maybe one or two of those new Walkers (and maybe we'll see some Bona Fide Hero on the sides ejecting from his fighter and hook himself up to one of those Walker's belly to... well... ok he won't have a Lightsaber to cut it open but he'll find a way, don't worry).
Again, in the teaser, that space battle... I'd go and guess that it's part of that battle on the surface... maybe (most likely in my mind anyway). The Resistance ships in space will probably be there of course to try and attack the First Order but I think that the major 'mission' there will be to ensure that Po can escape that mess safely-enough with Fin onboard (onboard of... dunno, surely not that X-Wing that blew up in the hangar... maybe the Falcon with Chewie or some generic more random Resistance ship... or another intact X-Wing).
Now, the only possible 'difference' between that battle and the Battle of Hoth is that I think that it might happen near or at the very end of the movie, instead of the beginning like in Empire Strikes Back. The thing is... Rey is in training at the beginning and probably at least until well into mid-way in the film. She'll eventually have visions about the upcoming attack on that base, or the coming 'danger', in general, to her friends. Then, the actual attack will start and then Rey will want to leave that island, mostly unprepared, to go to that planet where the battle occurs. Then again... just my guesses here obviously. It doesn't hold up THAT well since I know that they also need to show Ren enough for us to understand that he, too, trained with that old guy whose name I can never remember. So HIS training, however, might simply not happen on-screen and that would be a tremendously disappointing thing. But anyway... not sure where HE will fit in there screen-time wise and chronologically speaking. He might not show up at the beginning... or he may... not sure. I have to think more on that.
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Anyways, in conclusion... sure, I am genuinely interested. But, contrarily for Force Awakens NOW that we know what they did with it (turning it into A New Hope 2.0) and exactly because of that alone I DO fully expect The Last Jedi to end up being Empire Strikes Back 2.0. I and everyone else thinking this might be wrong. As I said earlier I HOPE to be proven wrong and to be very impressed by the movie. I hope that they go "bold" with it, that they try to actually push for NEW story elements that would then really distinguish this new Star Wars trilogy from the original one. But I am very hesitant in truly believing that any of that will really happen. That's because Disney seem to have adopted a very "cautious" and "traditional" approach in whatever CAN be 'new' to Star Wars canon. The impression I have is that they want the new generation of moviegoers and Star Wars fans to perceive Star Wars the exact same way that it was perceived when the original trilogy had finally been completed originally back in the early 1980's, only with a bunch of new characters, new names, new planets, new ship designs but with pretty much the exact same major types of events.
So anyway, yeah... I'm interested but... unfortunately, not more than that. Yes, I'll go watch it at the theaters, obviously, I'm not going to miss anything about Star Wars. But contrarily for Force Awakens I'm going in with actual low expectations. I went in with VERY high expectations for Force Awakens because I actually did NOT ever expect that one to end up being a retelling of a movie that had been made back in 1977 by someone else just for nostalgia's sake, and came out of the theaters just shaking my head in disbelief of what I had just watched being real to start with and supposedly being 'canon' to the Star Wars saga.