Well no, because the ETC also appears in WoW and we have multiple HotS abilities showing up in WoW on a consistent basis. Exuberance, Chrono Loop, Wailing Arrow, and The Hunt being the latest examples.
Borrowed heavily? Disintegrate comes from Kalecgos and the Blue Dragons;
They've been doing that ability for quite some time.
As for Rastakhan's Rumble, I'm all for deeper troll lore, however it is doubtful that we will get a troll-based expansion granting us a new troll race, and a troll based class. Thats a rather tall order.
Well no, because with the Crypt Lord we have a potential new race: Nerubians, a potential new class: Crypt Lords, and a potential expansion: Azjol Nerub/Spider Kingdom.
I will say that the ETC is far more of a long shot, but even that has more basis than what you're suggesting here; a broad class with no foundation, little lore, and bringing nothing to the table that can't be done by existing classes.
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TBF, I'm using the scientific method.
And yes, I would say being humanoid is a requirement due to armor and weapon concerns.