implement a game style where the goal is not to conquer all territories, but rather to hold a particular territory for a set amount of time. alliances and team work would certainly come into play here.

I like it.

I love it, would give some variance to the game. Maybe also a scenario like 3-on-3. Any other suggestions?

I like the idea but how should the players be rated?

Different kind of games could have separate ratings. I used to play a lot at the Free Internet Chess Server (Fics). They had different ratings for standard, blitz and I think also "wild" where wild include an entire array of bizarre chess variants.

Also 2-on-2-on-2 . And there is a subvariant - that you either know or don't know how the other alliances are arranged. If you don't know the other alliances - you only know your own ally.