I'm saying the following has little meaning:

The date of the MeeGo announcement is as relevant as Arbor Day or your best friend's birthday on the question of future, officially-supported OS upgrades for the N900. Prior to the MeeGo announcement, prior to the release of the N900, Maemo 6 was coming in the second half of 2010 and every indication Nokia had ever given pointed to it not running on the N900. The MeeGo announcement changed only the name of the software the N900 wouldn't be getting in an officially supported manner.

I think they see it more as a transitional piece, but yes, it's been clear since at least last summer, well before the release of the N900, that Harmattan (and its capacitive multitouch screen) was the mass market ready product Nokia wanted to be selling.

Nokia had made clear the future of all of the company--Symbian, Maemo, desktop apps, and beyond--was with Qt. They'd made clear Ofono was the telephony stack they wanted. And on and on. None of it was ready though, and they'd already rushed past Elephanta due to it being too small a step.

Fremantle and the N900 carried the existing Maemo market forward, giving developers something more modern (and GSM capable) than the N8x0s upon which to build, and expanded the userbase as well. And seeing how official Qt support on Maemo 5 has turned out to be far greater than was originally planned, the OS may live on a bit longer, and more comfortably, than originally thought.

Beyond that, the N900 has both the reference UX MeeGo and unofficial Harmattan-MeeGo in the works for it. "Don't count your chickens" certainly, but there have been a number of hints regarding those updates, particularly of Harmattan-MeeGo, that seem quite promising.