With Sony fully opening the crossplay doors, players are all in one single base now, where anyone can play with any other player, regardless of their platform. Just like in Fortnite's case, players can choose to opt in or out of crossplay on www.lolga.com the main menu.The RocketID system is still in the works though, so crossplay parties are still not available. Psyonix did say in their official announcement that this feature will come with the first update in 2019.
It is interesting that Sony are still calling the PS4 crossplay a "beta program" which means they haven't officially released it yet, nor do they officially support it as a full-fledged feature. Technically, this could mean the company is still working on polishing the system or that they still have a way to abandon it at some point down the road, should an opportunity present itself.
That is all speculation so far though, but the actual confirmed news look way better since PlayStation 4, Xbox One, PC and Nintendo Switch can all play Rocket League together now. It should have even fewer issues than Fortnite, since Rocket League should have fewer crutches for console players that others might find unfair.
Rocket League Items keeping the holiday gifts coming with a 2XP weekend event starting on Thursday.Psyonix held Rocket League first ever double-experience weekend back in October, and the developer is already following that event up with another weekend full of twice the experience. The announcement was shared several days ago, but the event is scheduled to start soon with 2XP being active during a long weekend starting tomorrow.