Blizzard tweets about plans to launch competitive play in Overwatch, saying "We'll be introducing our Competitive Play (hopefully) later in July," a change from their previously announced intention to get this going by the end of this month. A later tweet specifies: "We're aiming for mid-to-late July." In related news, Overwatch principle designer Geoff Goodman touches on balance changes for the multiplayer shooter in a couple of replies to a thread on the Overwatch forums on the topic. Blizzard has not discussed balance changes before, and this is not comprehensive, but he does specifically mention the possibility of nerfing McCree and buffing D.Va. This post about D.Va says that she probably need improvements, but based on the nature of the character he says that this is unlikely to be in the form of increased damage, and in this post he discusses corralling everyone's favorite cowboy:

I've been watching McCree carefully since we've released. McCree's flashbang plays an important role in being a strong option against very fast/agile teams (tracers/genjis/etc). It is also a nice tool to prevent close range devastating abilities and ultimates such as Reaper's Death Blossom.

That said, its probably a bit too good at dealing damage to higher health targets such as Tanks and barriers. I don't have any concrete changes yet, but I'm going to be testing some things internally to see how he plays.