At this point with the way egi's work now (basically being nonexistent since they don't take damage, can't be targeted, don't generate their own aggro, and only use a single auto attack on their own with all their other skills being on egi assault) I think the best way to go would just be to get rid of them altogether and replace egi assaults and enkindle with demi assaults that summon a demi version of various primals to do a single attack/ability similar to NIN's Hellfrog. Then they could easily swap out various primals for the three demi assaults in a number of different ways.

Alternatively they could actually make the egi's impactful by upgrading the egi assaults, tying them to aetherflow and dropping fester/painflare. It would reduce the insane number of ogcd's and make aetherflow feel like less of a completely separate mechanic. Of course that doesn't fix the issue with the egi themselves being a glorified autoattack for SMN.

Regardless I agree fully that they need to implement more primal options and with how minimal the impact of the egis currently is I feel now is the best time they could actually do it. The fact that they didn't even bother to give us a Sephirot egi glamor despite already having one in the game is pretty bad honestly and I can only hope the reason they didn't is because they are actually working on implementing something with them.