There's no current timeline for cross platform partying. We are patching in a way to do cross platform private matches soon.
Unfortunately cross-platform friends/party is a huge system and given we are both a small indie studio and weren't guaranteed cross-plat would even be approved, we chose to rely on Sony and Valve's systems instead. This brings a lot of reliability and allowed us to ship the game when we did, but rules out cross-plat partying unless we switch to a completely homegrown friends/party system. Right now that seems lower priority than other features on our plate like Ranked Teams, Tournaments, etc. but we're always listening to feedback.
Totally understandable and I agree that other stuff should have the priority.