Honestly summoner is a bit of a meme job at this point, but if they would give us the ability to change out the summons from ifrit titan and Garuda for any of the others it'd be better, at least thematically and aesthetically.
Granted, that'd be a ton of abilities in the spell book, but just that alone would sooth some wounds I think. I'd love to swap Phoenix out for Alexander and have Ramuh, leviathan, and Phoenix as my filler.