GURPS Survey
I was thinking recently that a TL 9-10 setting with a situation where enemies from an alternate dimension, or maybe even several, ala Torg, are invading the earth of the game, might be fun.
The characters would be elite operatives drawn from all over to resist the invaders. You could have martial artists, psis, biomodded spies or commandos, pretty much whatever you wanted to include, really.
Scenarios could range from straight up raids to recon missions, to diplomatic missions seeking allies against the invasion.