Consider this idea for FFX-3, Ultima:
If Will heavily implies the inclusion of more Summoners and it's possible to turn incarnate spirits into Fayth, wouldn't Seymour be perfect for Odin (like you said) but not as Yuna's Aeon (cuz unresolved sexual tension still exists between them, at least from Yuna's end), but Baralai?!?!? I mean, if Tidus winds up becoming Yuna's Fayth as Leviathan (kk's idea), then Seymour can totally be Baralai's.
Honestly, going from the Yevon's secret video, the two seemed to share some kind of mutual companionship (even if it was born for a mutual desire to use each other). Baralai changed so much from FFX to FFX-2, Nooj couldn't be the only reason he winded up like that. I mean, look at the way he talks! He sounds fancier, like he hung out with the Guado for too long. XD