I dont think the future of the n900 is as grim as some of the previous posters.

As for furture Maemo updates from nokia, I wouldnt expect more than 1 more if even that. I think they will begin putting all their effort into Meego. And dont forget that the developers of Meego are using the n900 as their development hardware platform. I think that means we can pretty safely assume a working version of Meego that has full or nearly full hardware support on the n900. The only issue i see is going to be apps. They are going to have to convence developers to either change to the meego platform and release their software, recompile qt apps from another platform, or completely port apps previously developed for another platform. And that the major flaw I see. There is just no visible benefit to leaving thriving markets (android, ios) and coming to meegos fledgling market place.

Now the underdog in all of this i think is NitDroid. They recently got froyo ported to the n900. They have partial hardware support. And some people have been able to access the android market place and download apps. If they can continue to improve the quality of the build and increase hardware support fully i think this could be a real contender for the n900 main OS.

If i had to put money on one of the above scenarios i think i'd have to go with NitDroid. But I am a sucker for the underdog.