Considering how big multiplayer games are and how fast PC and mobile are growing both in popularity and power, I don't see Sony's strategy lasting that long. Why would you want to get into a machine to play the latest MP game, when most of your friends are going to play elsewhere, and your console doesn't allow you to play with them? Considering how important is this kind of casual market for the Playstation brand now, I really doubt Sony's choices here will last further than this gen. Otherwise, they're going to start losing potential sales to other platforms.
PS4 is able to cross play with Mobile and with PC. It is not able to cross play with Xbox or Switch (specifically speaking about Fortnite here)
So Fortnite is basically this:
And it might even be: Xbox+Switch+PC+Mobile
Its a bit silly. Sadly, I started Fortnite on PS4 a few months back, so I am stuck on my island or with multiple accounts.