"The first step will be an open beta beginning today for Fortnite that will allow for cross platform gameplay, progression and commerce across PlayStation 4, Android, iOS, Nintendo Switch, Xbox One, Microsoft Windows, and Mac operating systems. We see the beta as an opportunity to conduct thorough testing that ensures cross-platform play is best on PlayStation, while being mindful about the user experience from both a technical and social perspective."
Looks like they've finally done something about it!
Read more at the PlayStation Blog
Great news and I hope it goes smoothly and comes to many more games. As it says progression and commerce will be crossplatform also I guess that means ps4 accounts will now (soon?) be usable on Xbox and Switch.
LTD: PS4 - 125m, Switch - 110m, XBO - 51m
2020: PS4 - 9m, Switch - 22.5m, XBO - 2.5m, PS5 - 4.5m, XBX - 2.8m