Seeing as how this is being handled by Vicarious Visions, I can't see this being a simple "remastering."
They can't just port the games like that. Not only is the architecture completely different now, but all 3 games are coded in Andy Gavin's GOOL, which only he truly know how to work with. Plus a lot of other technical details that are just too hard to program on today's technology.
If they're going to recreate the games (which seems like the likelihood), I doubt they'd stop at "exactly the same graphics and gameplay but in HD". And before you suggest emulators, remember that this is, according to Sony, being done from the ground up.
Those publishing rights would be irrelevant with a full remaster from the ground up. If the collection is PS4 exclusive, is because Sony paid for the exclusivity.