Ah, so Reisen comes here to tie up the Occult Ball plot.
At the very best Tasofro will release everything new to the PS4 version in a PC update, but that's honestly not generally how they do new version-exclusive features in Japan, especially if they are in Sony's pay. If they eventually make a full expansion pack or sequel down the line, Reisen is also guaranteed to be in it.
At the very worst, ULiL for PS4 will be the last Touhou fighting game in a while, and Reisen will stay a PS4 exclusive. This is not impossible - in the Strange Creator interview, Unabara said he had finally accomplished his goal in fighting game design with ULiL, and he may do something different next.