I really don't think the games could coexist together. But there's been some neat linking things in there. Like in FFVIII, in the northern part of the world, there's that huge mysterious crater that the Garden can't cross. Could the Planet still be healing it's wound in the Northern Crater? And then in FFX-2, Shinra spoke of all the energy in the Farplane and of how it could be harvested to be used as an energy source. I think those things are neat.