What are some of the most requested primals/Eidolons?

[Enkidoh]

I know Ultima has been featured in a variety of ways in the XIV world thus far, but I'd love a battle against her Final Fantasy 12 rendition: Ultima, the High Seraph.

Ultima is actually already in the game, but again not as a Primal, she is actually

an Ascian, you see her briefly talking with the other Ascians in the Chrysalis around the patch 2.2 storyline, although her name has been altered to the mistranslated 'Altima' from the original PS1 version of FF Tactics, possibly as a fanservice reference to the original version of that game but also probably to avoid player confusion with Ultima Weapon and the spell Ultima.

Either way, she's already in the game but not in a Primal form.