I'm PRETTY sure that one day a coder will be able to install it on an N900. i mean for gods sake, we installed windows xp, mac osx and some Linux platforms on n900. o yea and android is on n900
It's just a matter of someone getting off his/her *** and start working on it.. i would, but i dunno how :P maybe someday

So yea, i think that there will be something like windows 7 phone on N900.