An idea I keep having but never doing anything with: Game with two separate factions, one magical and one high-tech. Characters with powers are recruited by the former, characters without by the latter, and each side is told the other side is pure evil (and probably planning to destroy the PCs' homeworlds, to give them incentive), and are trained to fight a war that's really just a result of these two countries, or planets, or whatever having a massive grudge against each other.

Intra-faction CR would be the norm, but there would be opportunities for mingling (without the NPCs' knowledge) and for desertion.