I think it'd be cool, and balanced, to separate each summon so you can have 1 incarnate and say, one dragonling out at the same time. On lone wolf it sometimes feels limiting because they start off with 4 action points, 5 with haste buff, but when you're so used to having 6 it's depressing.
I honestly get way more out of fane using apotheosis time warp blood storm and grasp of the starved combo for instance, so as far as being overpowered I daresay this is the least problematic thing to consider.
Just reduce summon times, and maybe lower stats, or have a limit breach per 5 levels of summoning. So a lone wolf could have 4 pets maxed but only 2 for a nonbuffed 4 party crew character. But it would allow other summons to be used to create forced variety so you can't just pop 3 incarnate champs out like other mods are doing.
I think the spell variety of an intelligence mage is more involving than just dropping a summon and buffing it with the lower tier spells. Allowing me to use the different summons together would enhance my gameplay experience, and with proper balance, can make the summoning class a fun class to play.