Hmm, I like the idea of it, simply because it's a way to introduce the SMN class/job without disturbing the Lore. However, I think what they SHOULD do is introduce a series of summons to either mimic or parallel the primals.

For the mimic idea, they would be like vessels that take on the shape and styles of the primals.

For the parallel idea, they could come up with a series of summons that are the good, non-violent versions of the primals. And eventually, what they could do is whenever you beat some of the primal summons, you convert them to the "good side" and they are then summon-able.