Well, Savage Worlds: RIFTS does exist . . .
That said, outside of combat the core skill mechanic is pretty simple, and the powers/spells/psionics are effectively self contained rulesets. It's just combat that would break in half via PbP? The more I think about it a socially oriented palladium game might work pretty well; maybe it's a RP on the weave, run combats on discord sort of thing.