Psyonix has made a new deal with WWE, that will see WWE themed items added to the game. This was announced today, and the Items will be available this spring and specifics are not being shared right now. That said, more details will be shared in the future.
Rocket League will be playable at WrestleMania 34 in April, building on the healthy partnership deal that Psyonix established. Rocket League has previously been a major sponsor of WWE events, so this was inevitable.