> You can release a remaster of an old game, but any reverse-engineered version would be competing with it.

Technically, that's correct of course. But realistically, how many people will build one of these projects from the source code they obtained from GitHub, download the game assets from somewhere and spend a lot of time to make it all work on their machine instead of just buying the remastered version? Some, sure, but I don't see Rockstar losing a lot of money here.

If I were in their shoes I would simply hire these developers. And leave their fan projects alone as a sign of good-will and generosity towards the community.