Incorporating the remaining ARR primals as Egi's would be cool if they can differ between at least Garuda and Ifrit because there's probably no reason to have multiple Tank egi's such as adding debuffs like others have said. Not seeing a reason to include every primal ever as while Summoner has historically been about summoning some big thing who wants to try and work out which egi is good for a given situation with a billion egi's and that's not even getting into the development stuff?

Also getting a new summon ability every other level doesn't leave much room for non-summon abilities unless XIV makes like XV and goes beyond a level cap of 99 and even then at ten levels per expansion it would be messy.

A Phoenix Egi which already exists in-game (never seen it outside of its name on the enemy list) would be cool. Lower damage than Garuda-egi, but perhaps and maybe tied to a trait, a sort of auto-life ability for the summoner so if they die, the egi may die too and revive the summoner and put that summon ability on a cooldown or something to prevent a theoretically immortal summoner and keep it as a sort of oh shit button.