Looks like Sony might be loosing their grip a bit as today, Rocket League announced that starting today, the game will now feature full Cross-PLay between players on PlayStation 4, Nintendo Switch, Xbox One, and Steam PC. This is still in beta stages but will aloow players to randomly matchmake with or against each other in all Online match types (i.e. Casual, Competitive, and Extra Modes).
You however can’t make cross-platform parties yet however, though that is said to be in an upcoming update. You can still play with friends by joining or creating private matches.