Watch Dogs 2 has lots of forthcoming add-on content, and Ubisoft has been kind enough to lay it out for us in the form of a "content roadmap". There's stuff coming as soon as April, including a new PvP team-based mode called Showdown, as well as multiplayer motocross, eKart and drone races.
Meanwhile, in May, the No Compromise DLC pack will release, which adds a new single-player mission in the form of Moscow Gambit, as well as six single-player race time trials (with leaderboards) and a bunch of clothing sets.
It's the June stuff that's most interesting though, in particular support for 4-player parties "to explore the city and play activities together". That presumably doesn't include single-player missions, but instead all the side-quests and races.
The full rundown is available over on the Watch Dogs 2 blog.