Here's another thought .. we know there will be finishing moves, so what about sacrificing a downed enemy in order to summon daemons? The more powerful the enemy you defeat, the more, or more powerful, deamons you get to summon.

Or why not just sacrifice a multitude of enemies in a row to compensate for them not being as powerful

So, effectively build a pool of summoning points, which you could then use to to summon a pack of lesser daemons, or a single more powerful one? That'd work.

Maybe you couldn't summon more than one daemon at a time unless you had a soul ring or some kind of chaos gift that allowed you to store the souls of your enemy :3

Maybe allow Sorcerers to summong more / more powerful daemons than non Sorcerers?
Or make summoning a talent / path / upgrade (however these will be handled)?

Yea through the lore what it allows giving each race their own specific uniqueness.

I would say, YES. BUT only if the player has a set stat for the ability. Otherwise EVERYBODY would spawn daemons.

The summoning should only be used by Sorcerer classes. That and most daemons require a sacrifice, like Khorne needs Blood, Nurgle rotting flesh, etc. So they would need too offer some tribute before teh summoning.

I can just imagine it now...A daemon zerg rush...

This is fine, I used to sacrifice/possess a 25pt Lt. model so that I could bring a Greater Demon into the material plane.

Yes because I plan to be a Dark Apostle as well and overwhelm enemies with Daemons at my side.