And this is where I think of the game-side of games programming to be more an art form (I say this as an ex-professional game developer). GPT-3 could be used for narrative generation, environment generation, and adaptive AI, and these are all exciting areas for research and experimentation. But as you say, underneath is a solid engine, and one day an AI could feasibly build an engine from scratch, but I think that day is decades away. The AI that we have today are just toys.