Hm- maybe your experiences are different, but for projects I've worked on, the game state is way too complicated to be usefully inspected and manipulated with a REPL. Especially if you are doing any sort of data-oriented design such as SoA or ECS.

There are quite a lot of other complicated factors such as "what thread does this run on?" and "when?". When you are debugging and hit a breakpoint then you basically have a REPL in the Immediate window...