We kind of have a bunch of these guys left, in hindsight. Up to this point, we've killed three, but the Espers from XII that they're named after have at least 8 more members (Loghrif, Emet-Selch, Fandaniel, Pashtarot, Mitron, Emmerololth, Halmarut, Deudalephon). Then we also have Elidibus, that one Ascian from 1.0 that was also involved with Alexander, and, as of 4.4,
Solus
.

Elidibus and the last one on that list seem like they're shoe-ins for 5.0, but what about the rest of them? That feels like a lot to introduce suddenly. Would it be better to just put them into some kind of Normal/Alliance Raid and do a story akin to Coils that concludes their story satisfactorily? It's not as though Bahamut and Omega didn't have their plot relevance dealt with similarly.