If Demonic Rebirth procs you don't get any benefit from it when summoning a new pet in DA or Meta. You have to swap to normal form and back. It's a bit clunky in the middle of nuking someone in Meta or if you are getting nuked in DA. I think it would make sense to have it costs no fury when you have Demonic Rebirth and need a new pet in one of those two forms. It would still have the penalty of 1 minute summon cd, so it would not be completely cost free.
It would also be nice if we could cast all the non-damaging spells when transformed. I often lose Dark Intent to spellsteal spam and re-applying forces you to normal form.