This sounds great, but how does it actually work?
Let's say you've got friends you want to play with on XBL and you're on PSN or PC. How do you find friends that are on other chat/friends ecosystems?
I guess it works with Win10/XBL since they're both just Microsoft accounts (I even used my old XBL MS account when migrating to Win10).
I think Sony have just as much (if not more) to gain from this too. They have the most powerful console, so their marketing message would be, "You can now buy the best console and don't worry about leaving your friends behind".
MS will only really see a net gain if Sony refuse, since MS could then market Win10 cross-play as a killer feature.
I really hope this actually happens. My friends are split across multiple platforms, usually making multiplayer games too much effort. Co-ordinating a platform choice usually involves at least half my friends being unable/unwilling to play, and more often than not involves everyone deciding it's not worth the hassle outside of the most popular games like Destiny/Division/CoD/BF.
Allowing crossplay would make multiplayer so much more viable, which ultimately means more money for publishers that support it.