It appears that Fortnite, an Early Access game from Epic, temporarily allowed true cross play by having PSN and XB1 gamers playing together. Unfortunately it appears this was NOT intentional and it was later disabled.
https://kotaku.com/epic-accidentally-allows-xbox-and-ps4-cross-play-on-for-1818518611
Seriously, I just wish at this point that all the game publishers just say "F*ck you" to Sony and enable cross play on all their games. I mean, what is Sony going to do other than give them a reprimand? If they were to shut off the games, public backlash would be tremendous, more than it is already. I'm tired of this walled-garden gameplay. If Sony isn't willing to do it the easy way, then I say force them to do it the hard way.