It's like a gift that just keeps on giving.
Before we know it, we have raytracing, geomod and trading features, and the game world is adjusted to dynamically changing continuous environment driven by AI.
Nah. Seriously, though. Things like atmospheric flight support aren't that far-fetched. Full material system will mean that a lot of new content can be created and existing adjusted. Some kind of shadow mapping would be awesome at some point...
As to how long will FS2_Open continue to improve - as long as there's even one person willing to work on it. The community, now, that's a different matter... but I don't think it's in any danger of withering away too soon. We're way past critical mass of users to keep the boards active, and I think things will only improve with new total conversions drawing new blood in. Same goes for new features like better multiplayer code - if I'm not much mistaken, FS2 used to have fairly active multiplayer community, while with FS2_Open only a handful of players are doing it on a regular basis. Getting an active and relatively large multiplayer community working would be great.