I really like now that fortnite has cross play on PS4, but does that mean other games on PS4 could have cross play? The world may never know.
well... Probably not. For a Short time, Steam integrated Portal 2 with Steam and PlayStation 3. They could've done A LOT more... maybe another topic another time. While this connectivity still works for Portal 2, they just didn't keep it utilize it for other titles.
The partnership could've went very far... Half-Life 2, Left 4 Dead, Alien Swarm, and many other titles could've had cross play capabilities and extended the user base.