I don't think there was ever an explicit promise made to bring full portrait mode to the N900 - unfortunately I suspect people are going to latch onto this incorrect statement rather than the rest of your post. The history of maemo devices have always been in landscape, the N900 is the first to be phone sized. The N900 finds itself in the awkward position of being placed in the phone sector but with an OS that was designed exclusively for landscape use, developed by a team that don't understand how to or why they should bring portrait elements like a simple OS wide portrait keyboard. When I bought the N900 a Nokia rep did tell me that portrait would be coming, but as with anything Nokia unless you hear it officially and communicated from the team actually developing the thing you should treat it as speculation.

In regards to the rest of your post, you'll find a lot of opinions already registered by searching through the forum - there are already a lot of threads and hundred of pages covering the same info. In regard to Nokia N900 support going forward you should, imo, consider it as complete now as it ever will be. It's been sunsetting since the MeeGo announcement.

Enjoy it for what you have now