Tri-Stat is low on my list of priorities, because its point-buy system requires more oversight than Hero or Mutants and Masterminds.
M&M is pretty flexible; it just came out with a fantasy setting using the same superhero engine. A number of powers would have to be ruled out for balance reasons, but I think it could work. The main worry I have is that since I'd be ruling out 75% of powers as too 'superheroey', that my players might feel restricted or end up with similar builds. It would definitely work, but I'm hoping someone will suggests a better fit.