Even though they don't see it happening anytime soon, the Overwatch team is open to having a map editor in the game. Blizzard's Jeff Kaplan had the following to say in regards to a question posed by a fan about whether players would be able to create their own maps for custom games in Overwatch:
"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."
The fact the feature is on the road map is promising, but don't expect this feature anytime soon. As Kaplan said, while it may be something the Overwatch team can do, it's not necessarily easy to accomplish. It's typically not about whether or not you currently have the ability to make maps in the game, but rather how accessible and easy that software is to use for a casual audience. If you're making something that's too hard to use, you won't have a variety of maps. Good on Blizzard for being upfront about where they are in the process as opposed to vaguely teasing something for people to ask ad-nauseam every time there is a Q&A.
