To sum up:
All 3 consoles have had PC Console cross play. (and with their own offspring as well)
MS says:
We’re enabling developers to support cross-network play as well. Of course, it’s up to game developers to support this feature.
Sony says:
We would be happy to have the conversation with any publishers or developers who are interested in cross platform play.
So, developers get on it.
And MS, get on with those cross platform Minecraft saves so I can load my ps4 save on PC and iPad :)