I particularly like this one. When our group moved to a new alliance all together and had to start over on titans, just for fun we set team power restrictions on teams for titan hits so we wouldn’t wipe them out before everyone had a chance to hit a couple times. We found it inspired a lot of creativity, and mixing and matching odd combinations of stars, leveling, and troops that you wouldn’t normally consider. It was honestly some of the most fun I’ve ever had in this game.
I think the posts above cover most possible variations on team limits, other than perhaps classes when they’re released, Atlantis family, or only “regular” season 1 tc20 heroes.
Of those, I think it’d be nice to see opportunities to use only tc20 heroes every now and then, as a way to provide opportunities for players who don’t have a lot of strong HOTM or S2 draws.