And some paid DLC to go along with it.
http://www.nintendoworldreport.com/news/56799/streets-of-rage-4-receiving-major-update-later-this-year
More content is coming to Streets of Rage 4 later this year.
A major update is planned that will include a training mode, a new ultra-hard "Mania+" difficulty, and new color palettes for the playable characters plus support for the "Mr. X Nightmare" DLC. This DLC will include a Survival mode and three new playable characters.
The first character - major foe Estel - and hints for the other two are in the below trailer: