From GameWatcher: “If you’ve been with Rocket League ever since its inception to the market back in 2015, then by now you might be thinking of the game’s inevitable successor, the theoretical Rocket League 2. Should that be the case, rest easy, because no such thing is even being planned by the developer, Psyonix, as it currently stands.”
Source: N4G PC Psyonix Says Rocket League 2 Unlikely to Happen