What's the harm with having the "legacy" posts to start with? Several vBulletin sites I've used in the past have archived old posts (eg. TiVo Community which has done this twice). Perhaps once MeeGo launches "for real" an archive could be created of the very old Maemo posts?

From what I understand, Maemo5 will become compatible with MeeGo (to a large extent, at least at API level) which will blur the line between "Maemo stuff" and "MeeGo stuff" - this could be a good thing, it just needs to be managed appropriately. As time progresses, the "Maemo Stuff" will most likely reduce, as has happened with the 770, then N8x0 discussions here.