IDK where you guys got that 2.5 was the end of the content patches till expansion but, well, ok.

First off lets talk about what is a primal and what not.

Primal are undying entities SUMMONED by their followers gathering vast ammounts of aetherite. By this rule, in game we have: Ifrit, Titan, Garuda, Leviathan, Ramuh.
Elder Primals are the same but they don`t need to be summoned by anyone, can perfectly become manifest by themselves as long as they are not imprisoned somehow: Bahamut and Odin.
Behemonth is not a primal. Shiva, till we don`t know how she made it to Ishgard is not a primal. (doesnt have a "tribe" so she could perfectly be an elder primal). King mog is "considered" a primal but is more of a god summoned by faith than other thing.
Any voidsent isn`t a primal, for example, Diabolos.

So, for what is Eorzea, considering the other potential "beast tribes" (gigas for example) there is pretty much a lot of lore to get more primals from.

The theory of Ishgard being Alexander is... IDK, hard to belive, why he hasn`t awakend yet? if he is a primal, Ishgardians with their zealot for Halone will never be able to summon him so that denies it`s existence right away in the game, if he is an elder primal there is no reason for him to not have awaken in all these years, specially since Alexander, Odin and Bahamut form the most iconic fantasy trinity of them all, the Castle, the Knight and the Dragon. So, if 2 of them are arround, or have been arround, why Alexander doesn`t?

And what about the "confirmed" Fenrir? Also in one interview yoshida said that Odin would eventually become "more important". He is an Elder Primal ffs, you can`t just leave him wandering through the shroud slaying adventurer just because.