I'm not sure that we are getting all the information, at least to how extensive the product will ultimately be. All we know is that they are releasing a small region to fly in for free. For all we know, this could just be a precursor or demo for a much larger project that is still 1-2 years from release. The MS Flight website has not exactly been a gold mine of information. They went from merely admitting the existance of MS Flight to saying they are going to have some sort of flyable area soon. Maybe I've been living under a rock, but I haven't seen any interviews or third party coverage yet.
The good news is that FSX has legs and tech is finally catching up. It's still a pig from an optimization stand point, but it's about as feature rich as it can get for the moment and some very high quality payware addons have been release and are planned. Hopefully we will have a better answer for a FSX successor in the next couple years, either from Microsoft or possible another developer.
In the mean time, I finally ordered my Thrustmaster Warthog HOTAS so I'll be knee deep in BS2, A10 and FSX/PMDG 737X for the forseeable future. I'm a happy camper.