LLMs have changed the obstacle of doing something from (time, attention, expertise) to (time, attention, tokens).

I don't see what's unique about GTA6. It's just larger in scope if you wanted to decompile or greenfield a custom engine.

But at the end of the day you'll be able to unpack the assets yourself and immediately have the worldmap running in a browser in Three.js. And once you're there, you can vibe-code any game you want on top of it.