Chromie in HotS is essentially just a uno-card Mage, I dont really see where her kit is unique at all compared to an Arcane Mage.
Her Q and W are as basic abilities as it gets, her E is just a glorified non-attackable Frost Nova + Deepfreeze, and her second Ult is essentially Alter Time but for the enemy.
I think people put far too much emphasis on the word Envoker.
The Class will very likely be called Invoker during development cycles due to it invoking three of the Dragonflights powers.
I doubt they'll go lower or above that and just let the Class sit at 3 specs.
Black: Tank or DPS Agility Melee
Bronze: Ranged/DPS Intelligence Caster
The only important question is if its gonna be Red or Green Dragonflight for the healing spec. I would say that Blue is out since its nothing else but a Mage, and with Ysera being essentially "dead" in Ardenweald (and touching a bit too close to Druids), the only living Dragonflight Leaders we have are Wrathion, Nozdormu and Alexstrasza.
So the healing spec is gonna be Red Dragonflight, possibly how its handled in HotS, dealing fire DoT damage to support, somewhat in the way of a Disc Priest, and to heal your teammates.
Theoretically they could stretch this Class up to five specs and include all Dragonflights but we gotta be realistic and honest here, this is Blizzard we are talking about. I am not even certain if it will even get 3. Maybe less specs would be for the better considering what for a design and gameplay failure Demon Hunter is.
Either way, if you cannot transform to a Dragon in Combat, its gonna be rather meh in the end anyway imo, unless the customizations with a Tail, Scales and Horns will make up for it. But knowing Blizzard and with Dragons being too big, and a scaled down Dragon Form looking too weird (not to mention 20 of them in a Raid), it's probably just the Flight Form.