Rocket League developer Psyonix has said that its interests right now remain on building on the first game's experience rather than working on a direct sequel to the game.
Rocket League is one of the biggest success stories in the last few years. The cars-meets-soccer idea sounded a bit silly to begin with, but it has now gone on to be a huge success story and one of the biggest multiplayer experiences out there. That being the case, it made its debut around 3 years ago, so it's not unreasonable that some might be turning their attention to a possible sequel.
For those of you who are, it might be worth tempering your expectations. Speaking to Gamespot, the game's director Scott Rudi said that the current plans for the franchise are to keep it a games-as-service experience. Explaining he wants to keep players engaged for years to come, he went on to say:
We want to keep this going. I don't know what I'd do with Rocket League 2. I'd rather do more to expand the exisiting Rocket League. It's doing great, there is a lot ahead of it. So yeah, we have no plans for Rocket League 2.
I can definitely see the reasoning here as it's clear Rocket League still has a large community. The game has a good art style so it doesn't look dated yet and there doesn't seem like there would be a huge benefit to scrapping all the work the team has done on the game. That said, perhaps the day will come when it is wanted. For now, I wouldn't expect a sequel anytime soon.