Inclusion of a map editor is a posibility, but not any time soon
Overwatch game director Jeff Kaplan took the time to shed some light on certain aspects of the game's future in a post on the forums. Specifically, he outlined the development team's wishes and ideas for future map modding and creation features.
"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."