If you ask me, Roux has as much potential as Fridrich, and Petrus and ZZ have a bit less potential. Of course, this is all completely unprovable. For larger cubes, the best method is probably going to be relatively efficient with an easy start and few slice turns - so probably a Fridrich or Petrus variant.
As for the future, I pretty much agree with Escher. I don't think people will move towards more algs as such, but rather towards a greater understanding of how to affect future pieces without wasting too much turns. We'll see more and more tricks such as multislotting, LS+LL techniques (ZBLLs, certain F2L+OLL cases, etc), and following/inserting more F2L pairs at the start. You can already see the fastest people doing this kind of thing, and since it seems to help there's no reason it won't increase in the future. Alg experience will help shave off tenths of a second just as much as turning speed will.