I'm not sure if you remember the entire history of the Metamorphosis spell for Warlocks, but from the time it was introduced, to the MoP revamp it has always been thrown in there because... well... Illidan. Now, don't get me wrong. I like Illidan. And before Demonology landed as a proper 'Conjurer' (back when it was a schizophrenic mess) I was suggesting that Demonology be made into a Demon Hunter -esque melee dps spec (I still wouldn't mind that alternative, if people want to keep pure dps classes pure). It just seems to me, that if we are getting more room with an additional spec, that we should take the opportunity to both: Flesh out Demonology's new direction to fully encompass being a Fel Conjurer, and give Metamorphosis a chance to shine with a spec fully designed around it. I would play both.