My purpose would be to create a multiplayer game programming platform. Basically, it would come with a game loop already running, with communications already working. Then you could modify the game by changing functions that transform game tick N to game tick N+1.

There's another way to do this. Just scan the compiled code for access to anything other than a fairly short whitelist of functions. This is how Terrarium worked.

Yup, this is the better approach to sandboxing. You can always expand a whitelist, but it’s not so easy to play black-a-mole.