I'm not sure why people are thinking XB1/PS4 cross-platform play can't happen, unless MS is lying about allowing true cross-platform play and sticking on other requirements like W10 integration.
FFXI allowed PS2 and 360 players to play together when MS was making exceptions to their rules to gain marketshare, FFXIV didn't come to XB1 only because of MS's policies on cross-platform play:
Source for the quote is a banned Dualshock site. Google it if you'd like.
And of course,
Nintendo has OK'd cross-platform play and games play with Sony platforms just fine. So, according to the information we have:
- Xbox and PS ecosystems have interacted in the past, before MS fully instituted it's walled garden approach.
- Sony currently allows cross-platform play with other consoles.
- MS
appears to have changed their policy about cross-platform play, allowing any platform to interact with their box.
Assuming MS isn't lying, cross-platform play is inevitable for the devs that want to use it.
EDIT: Yeah, and according to that Reddit thing, it looks like MS isn't lying.