Aahah this thread continues to get bumped up
Imo they got caught off guard by the negative reception this got when they announced it at the PSX and they're trying to add a few exclusive features to the PS4 version to justify its existence.
Obviously not major things but something like cross saves with the digital PS1 version, PS4 digital themes, support to DS4 controls. Still the game desperately needs to get better filtering for the low res backgrounds :/