As with all Blizzard games, people are working hard on their cosplay ready for the next conventions and such. I'm not into it myself but love looking at all the end products. I'll list all that I find for either people interested in viewing or for people looking for ideas.
Of course feel free to post any you've done or have found.
Reinhardt by Davence
Mercy by N_FX_Cosplay
Mercy by @allebrett