Clearly PS4 are wrong to deny crossplay, but looking at it from their own selfish POV, why would they give up such a huge advantage? I stayed on Xbox for far longer than I really wanted, purely because my friends were all on Xbox 360. I ultimately got a second hand PS3 at the backend of the generation to try the exclusives and was so impressed by the games that I felt extremely sad about what to do come the next generation, as I couldn't afford both consoles year 1.
Ultimately my friends also felt impressed by the exclusive games on the PS3 and all switched to PS4 at launch (Microsofts epic fail at that e3 helped that decision so much, but that's another story). If Crossplay was a thing then I'd have switched far sooner. Given how PS4 are the leading console system right now, they will have many users in the same boat, who will stay or come to the PS ecosystem purely because that is where their friends reside. I can't see how Sony would want to throw that away, neither would Microsoft or Nintendo if the roles were reversed.
Like I said, I would love to see crossplay, but people just don't seem to understand why Sony wouldn't want to do it.
I also don't really get the whole argument about families playing on all different systems. How many games actually work on an ipad/switch with the same feature set as Xbox one/Ps4 to the point that they would become crossplay compatible? Yeah, basic games like Fortnite will work because they port well but who's really gonna play Destiny or Anthem on an iPad?