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.
Yeah, for that reason it won't last once their total share of the market decreases further, but for now it's actually precisely that reasoning that has lead them to refuse cross platform play. When you have such an enormous share of the market it just makes sense to let everyone know that if they want to play with their friends (which will more often than not be playing on the PS4), you have to get a PS4 and not one of their competitors.
Like I said, when you're on top you can use slimy tactics like that to try to remain on top, and lord knows Microsoft and Nintendo would probably do similarly in the same position. Once their share of the pie shrinks further, though, they'll abandon that approach.