GTA 5 already has next-gen looking graphics, even if they ported it to the ps4, they wouldn't change much about the game.
And honestly? They got enough profit solely from the PS3/360 version, I don't even think they'll bother porting it to the PC, leave alone the PS4.
You might aswell wait for GTA 6, by that time, they might release GTA 5 for PS4, or maybe as a Gaikai version