Err... out of all the things you said the only thing that could possibly be true is the bug fixes.

If the QT cross-compatibility plan works out then the N900 running Maemo 5 (or Mer or if it does get Meego) will be able to run any QT app that any Meego variant runs (Meego itself is not a specific OS it seems, since they plan on it being installable on a variety of devices). So that solves the software issue. Sure some things may not work (e.g. if an app uses multitouch) but that wouldn't work even if you could upgrade the N900 to a Meego device.

And I haven't read anywhere that Nokia promised the N900 would get Meego or Maemo 6 (before the Meego announcement).

Like I said before to another user, you need to seperate software from the OS. Think of it this way, if you have a computer that runs Windows XP, just because it doesn't run Windows 7 doesn't mean it can't run the same apps, as long as the libraries they are based off of are the same.