We can hope for Maemo 5 to be supported by a dedicated team for quite a long time and have a MeeGo development platform on the N900, but not a full, Nokia-supported upgrade path with Maemo5-like functionality and proprietary applications. This is how this business works, but also because of the multitouch capacitive screen the MeeGo device is going to have (this is confirmed), some (maybe many) usage scenarios will simply not function on a resistive, single touch device. So an official upgrade path is a no-no. Everyone is invited to install the MeeGo image with Handset UX, but don't expect much.

I will be glad to be proven otherwise, but that's how I see it and I think it's closer to reality than many of you imagine.