Hereos of the Storm launched closed beta this week, and while there are no plans to add Overwatch characters to the game (at least until after Overwatch launches) there is a small easter egg in the update.
Tychus got a skin update and his color variants provide a couple images of Overwatch characters on them.
Here is the original default skin Tychus has:
The first color variant – as you can see, our favorite Overwatch assassin Widow makes an appearance on his left shoulder
The 2nd color variant displays who has basically been the face of Overwatch, Tracer.