Jeff Kaplan has taken to the Overwatch forum to let players know that Blizzard is entertaining the idea of allowing players to create their own custom maps via an editor. Kaplan's post came as part of a larger discussion of map editors by the community.
We are extremely open-minded about releasing a map editor for Overwatch someday. But because Overwatch was made with a brand new engine, this is not a small task or one which can happen any time soon. We have this on our long-term road map and believe heavily in user-made content. But there are many challenges ahead of us and it will be a very long road before our editor can be made available to the public.
This builds on the recently release map options tools that allows players to tinker with game settings to make custom matches.
Source: Overwatch forum