According to Rocket League Credits  a recent Rocket League leak in the Apple v Epic Games court case, there are Rocket League games in development, one being Rocket League Sideswipe.

Out of all of Epic Games’ excessive-profile pickups through the years, its acquisition of Psyonix and Rocket League can be one of the most fruitful. The rocket-powered car footie game isn't showing any signs and symptoms of slowing down each time quickly, capabilities a number of the first-class and most complete pass-play capabilities, and receives season after season of delightful content and demanding situations to maintain matters exciting, as if the middle sport didn’t already. However, one untapped market for Rocket League has been mobile and if latest leaked documents from the Epic Games v Apple court case are any indication, it appears Psyonix intends to LOLGA.COM deal with this twofold.