So perhaps we can discuss which "tribes" could need some more attention ...?
1. Religious People: I don't think an existing religion would be good in the game, but I support a fantasy religion with temple lot type, preacher career, monks, prayers an rites. This could bring great new gameplay opportunities.
2. Elders: Considering the young fanbase, a pack for elders would probably not sell well. Some exclusive "elder gameplay" would nevertheless be nice - bingo afternoons, teenagers visiting and supporting elders in the neighbourhood ...
3. Non-western cultures/peoples: EA has done this with mixed results. While I like the Japanese theme and the Asian vibes in SE and CL, the Polynesian setting in Island Living is just a beautiful stage for nothing. Packs with American or Australian native people could be interesting, but the question is what specific gameplay they could bring. Worldwide archtitecture and fashion is of course always welcome and can be added in Kits (like the really wonderful Moroccan Kit).
4. Disabled persons. I hope they will be added because many players want them. The challenge here is that they require lots of new animations for relatively little new gameplay. But videogame technology moves forward, so it may be possible soon.
