Funny you should ask.... we've been discussing this over in the Lore forum and there's a definite candidate.
(Well, okay, I'm one of the main people arguing for it. But still.)
Back in 4.4, when we were trying to guess who the mysterious voice might be, I suggested it might be him - mostly inspired by one of the alleged-leaks saying there would be something involving the Crystal Tower in 5.0, and the voice seemed like it would suit him.
And
then we get this poster. Credit goes to Fenral for picking up on the resemblance - I'd glanced over it and assumed the figure was female, then didn't think too much more about it until he pointed it out.
So I'm looking forward to finding out what's going on!
Regardless of who it is, I don't think the robes look particularly Ascian besides the hood - which could be just to keep their identity concealed for the poster.