Kind of like Moggle Mog's fight, except instead of moogles you have full primals. Imagine that chaos that would be Ifrit, Titan, Garuda, Leviathan, Ramuh, and (in the future) Shiva all at the same time. The combination attacks that Ultima uses are a large part of what made the fight fun to me and would like to see more.

And for the lore addicts, I don't think there would be a problem with the primals banding together, considering Ifrit, Titan, and Garuda tried that (and failed) against Ultima.