I hope they allow the account purchases to work cross platform. I even think they might.
However I really don't believe they will allow crossplay! They benefit so much all the time from NOT allowing crossplay, it would actively hurt their sales a lot, hardware and software. The sales data from the store I work at shows that a very large proportion of PS4 sales come from Xbox One trade ins, I know from personally dealing with many of them that it's almost always kids wanting to swap platform only because their friends all play PS4 together (usually Fortnite, but also things like Rocket League and Minecraft) and they are left out because they are on Xbox and can't crossplay. So they swap to PS4 so they can join in, and then going forward buy multiplatform games on their PS4 etc.
It happens at least once every single day I work, which is just a little store in a little town in the U.K., so if that's representative of what happens everywhere just imagine how many sales that's translates to in every store, in every country the world over. (And subsequently how many extra software sales are garnered). Allow crossplay and these kids don't need to swap systems. Lots of sales lost there. They aren't going to do that, it's far worse for business than a bit of negative press over not allowing crossplay.