I like that idea. I think that the Final Aeon would emphasize one attribute based on the character over all other attributes, so you're right that Tidus would be very stealthy and speedy like Gilgamesh.
Asura has made a similar appearance to Kali in some of the Final Fantasy games.
I am not sure on what Seymour would look like as a Final Aeon. I think that he may take on a form similar to Anima, but, at the same time, I think he would look less tortured and more willing to inflict pain on his opponents.








