Yeah I like the reasoning above, changing prediction to Kel'Thuzad or hearthstone innkeeper.
D. Va would be fine, the main thing we need is another main tank. If they make her bump a stun+reposition like Condemn she might be a suitable next addition to the roster.
Im pretty sure the next hero is D'Va since for sometime her voice files are in game files.
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D'Va skin tints for Kerrigan have been datamined, which to my eyes puts doubt on D'Va being her own hero so quickly.
Just remember, no longer being limited to just 3 colour tints per skin gives them more options to make those lookalikes.
Queen Of Ghosts -> Legion's Queen(Revamped Succubi) -> Cheerleader and now D'Va alike?
Also they might made D'Va but i guess it might happend later, but might work as Kled/Nidalee from LoL with her mech? If not D'Va now, im not risking now with my theories though.