This could be complete BS, and if so I apologise, but since ghost war launch, I have heard the PC community complain a lot regarding cheating and aimbots. (I know the division suffered the same issues for a long time. If so I would probably prefer to keep the console world separated from PC). However, I do believe that connecting the PS4 players to the Xbox players can only be a good thing, and enhance the lifetime of player base experience and lifespan.
Apparently crossplay isn't from the game developer itself. It requires another work from the platform themselves, in this case Sony and whatever they would like us to crossplay with.
Rocket League on PS4 has been doing crossplay with PC version. Though we must take note that that doesn't mean cross-progress as your game progression will still be separated in two platforms.
As for Fortnite, as far as I know, currently it's only the Battle Royale that Sony agrees to crossplay and do test run with. And that's Fortnite, you know, it has massive userbase that willing to happily roll their money. Too big for Sony to miss. If we haven't even seen other successful PvP games like Overwatch and R6S doing crossplay, it would be quite a hefty expectation to see it coming to GRW - especially the co-op, because when that happens, I would be back helping others (read: reviving others) from different platforms through matchmaking even though it's going to be Tier One Grenade Launcher-fest again.