Agreed, it won't be easy. I've been saying for some time now that people need to start understanding how difficult it is to develop new processors.
I actually have been saying mGPU the whole time, as that's what it literally is or likely will be initially (since I think we'll see GPU chiplets before we see them break the GPUs into dedicated co-processing blocks). But GPUs would obviously have their designs tailored for chiplets, so its really arguing semantics for no good reason.
He's trying to tell people that its not going to magically happen and work flawlessly, which I don't think anyone is saying, but he's responding to the general optimism that we are having that they will develop GPU chiplets.
Which as far as mGPU goes, the main sticking point is software optimization, and I think that isn't as much of a hurdle as he seems to think, especially if the platform provides some way of getting a pretty easy 50+% performance (which is where mGPU is kinda at right now, its just that GPU costs have gone so crazy that people don't want to deal with paying double to deal with headaches on top of the diminishing returns). If mGPU helps to lower the cost per GPU then it'd be more acceptable for consumers. The big companies doing the platforms (Microsoft, Sony, Google, Apple, etc) have the clout to make it worthwhile for developers to implement, and they also have developers of their own to make it easier to implement. I personally think a console would be a potential area as well, as the platform gives them a very fixed target, and Microsoft and Sony already provide a lot of tools to developers. On PC that falls to AMD and Nvidia, and the latter has openly kinda given up on most mGPU, while the former just leaves it up to developers (which isn't the best; AMD has been trying to change so we'll see, but if one of the next consoles has mGPU of some sort, it could mean its potentially easier to implement on the PC side).
I mean, we had mGPU working pretty well before. And we've been told it actually should be better/easier to implement on newer APIs. Plus we have other things that make it potentially more viable (VR headsets where they can do per eye rendering). I feel like we just need pricing to improve and normalize, and then a killer app to make people want the absolute best. Its like we need a Crysis type of game, or some VR thing.
Gaming is so fickle. I mean people were buying 3 monitors for Eyefinity and not balking at the costs that much. But now we have VR which is better than multi-monitor gaming, and people complain about its costs even though its similar. And the GPU hardware costs really have not changed that much (and arguably are not nearly that bad when taking inflation into account). But games just don't seem to get the same hype as they used to, or maybe its the baseline hype is higher so the relative peak doesn't seem so. Crysis really overshadowed everything although I don't know it actually did that well. We need another game like that though. Probably the closest we'll get is Cyberpunk 2077.