The lore requirements on a primal seem to be (1) ideas, and (2) aether. I don't see anything stopping them from making instances of primals out of carbuncles, trash monsters, bosses, kings, stones, or whatever. If summoners and arcanists are already using ideas and aether to make creatures, a primal seems like a natural extension.

Sadly, there's a lack of gameplay precedent for some of that.