Pretty sure the numbers were crunched long ago, as Playstation has supported cross-plat since the PS2 days. At launch, there were already Cross-plat games on PS4, such as War Thunder, and for the briefest of moments, account sharing on Warframe (Update versions made that impossible after a while, but DE hopes to bring something like that back). Heck, Rocket League had PC cross-play since the day it launched as a free game on PS4.

Since PS4 sales are over 2:1 of Xbone sales, Cross-plat gameplay has zero benefit for Sony. They have the bigger populations across the board, and no Windows-10 requirement. Xbone, as the more historically restrictive platform (one of the reasons that FF XIV and War Thunder devs refused to launch on Xbone), needs cross-plat for its games to have significant populations (especially at launch), and in order to sway folks thinking of going over to PS4.

I'd love console cross-play, but the smart thing for Sony to do is to ignore the pleas. They've already won.

That said, I wouldn't be entirely surprised if they allowed it for a few non-AAA games, but that alone would cause countless issues in terms of UI, security, etc...