So much finger pointing without knowing all info.

Right now the side holding up crossplay is: both.

PS4 has only allowed crossplay of Fortnite as a beta test that is currently ongoing, depending on that beta test Sony will decide whether they want to allow crossplay with more titles, this beta started in late September and there has been no update since.

On the Xbox side the issues have been listed already, Microsoft would have to waive the live sub requirement for FFXIV (something they have yet to allow for any game) and I can't find any info whether the xbox-only servers is still a requirement, though this one I find it easy to be waived.