The company typically goes for straight rereleases over updated games, as seen with the previous LA Noire and Red Dead Redemption ports (the latter of which did get a 60fps patch, to be fair). So if and when a GTA 4 re-release does come to pass, I'd put my money on it being a port with minimal improvements over a full remaster situation.

You'll have to wait longer to play a crime duo wreaking havoc through the streets of Vice City in Grand Theft Auto. Here's when GTA 6 will release.