The Oasis map should be available early next year with additional tweaks to the gameplay.
Blizzard released a developer update video in which Jeff Kaplan, director of Overwatch, discusses with a bit of details what’s planned next for the game in 2017. (huh, “Director of Overwatch,” that’s an entry good for a resume…)
Kaplan confirms that there are various characters and maps at various stages of development. As he mentions, at this stage it’s not confirmed that every idea will appear in the game.
The game was originally released in May 2016. Since then two new characters were added with new modes, maps and seasonal events. If you are interested in the future of Overwatch, there’s a nice video to watch: