The cross-party functionality was discussed yesterday from xingwang's blog

Game Director Scott Rudi also confirmed that a new Rocket ID system will soon be implemented into the game to allow players to party up with those on PC and Nintendo Switch. There will also be improvements to Rocket League Items how players level up to "make it more rewarding", as well as the previously announced Rocket Pass.Finally, Xbox One X enhancements will be arriving later this year with an estimated release date to be announced in the next few months. We'll be sure to let you know as soon as we hear more.

Rocket League’s cross-platform support is coming to different platforms this summer with Xbox One, Nintendo Switch, and PC players able to party up while they play together.The cross-party functionality was discussed yesterday in the latest episode of Inside Xbox, a weekly series full of Xbox announcements. Scott Rudi, game director for Rocket League, came on during the show to talk about everything that Psyonix has planned for the game during the summer. After mentioning the new Jurassic Car Pack and the anniversary event that’s going on right now, Rudi discussed what’s planned beyond the recent events.