They've done this, but unfortunately with Dissidia and its prequel. The story basically is that Garland from FF1, who became Chaos, was fucking shit up in some dimension/planet and was opposed by some chick named Cosmos. Chaos pulled in villains (Kefka, Sephiroth, Golbez, etc) and Cosmos pulls in heroes (Cecil, Terra, Tidus, etc). Had it been an actual RPG, it could have had potential, but it was some sort of fighting/action game hybrid with RPG elements that didn't really work out.
Anyway, FFX and X-2 are fucking great. I'll definitely be using Japanese VA though, as Yuna (and to Tidus to a lesser extent) are hard to fucking handle with their English VA.