*But it's shit
http://us.battle.net/forums/en/overwatch/topic/20746784507?page=3#post-54
Overwatch has 21:9 support on the PTR now, it seems.
EDIT :
As I feared. Instead of gaining image on the side, you lose image on the top and bottoms. Playing in 21:9 reduces your field of view.
16:9
21:9
It's not a minor drop in FOV either. You lose a significant portion of the image; almost up to 30% of it at the same FOV.

http://us.battle.net/forums/en/overwatch/topic/20746784507?page=3#post-54