There are supposedly lot of things still not hashed out yet, with the sim still being up to another year away from release (it hasn't even entered alpha testing yet, let alone beta). The Microsoft representatives have stated that their main focus for everything that has gone into this sim is the hard-core PC flight simmers, and they're placing a lot of importance on supporting addon developers, and will be discussing the SDK in the future.
https://www.youtube.com/watch?v=nmfmYfXOI1w
Everything I have seen/heard thus far has really left me gobsmacked, especially so since they are running it top line on a currently rather reasonable system. I'm amazed by the new standard of atmospherics, the scenery (and especially the way it is produced), the water, sky and clouds, weather, etc. - it looks and acts so much closer to reality than any other sim that has come before, and I don't see how any other current sim, in their current structure, could come close to matching it. Just the video/screenshots shown thus far illustrate how vastly immersive the sim experience is/will be.
I have seen several videos by those who got an early, unrestricted hands-on look at the sim back in September, and among so many other topics, they all touch on the new flight dynamics. There has been a lot mentioned about how the new flight modeling is fed by over 1000 data points spread across all the surfaces of the model, interpreting how those various surfaces are interacting with the air around them (including wind and air density), and that the aircraft no longer act/feel as if they are on rails. Among other things, it allows for far more accurate stall and spin characteristics, and accelerated stalls, with the surfaces of the aircraft's wing, fuselage, tail truly being taken into account in various angles of attack, turns, and slips (stalling differently/accurately depending on which surfaces are or are not creating lift and drag at any given time, as well as taking into account g-loading and side-loads/forces, etc.). I've also heard that they have more accurate ground friction modeling now too, which also takes into account the nature and conditions of the surfaces the aircraft is traversing. I've also heard a lot of good about the new sound engine and the quality of the sounds, and the new dynamic sounds, such as sounds from rolling over the runway or terrain, sounds from being bumped around by turbulence, etc.
