Interesting idea, and would make for one hell of a night……but if every power had to take the time to write down every move, it might take a while unless they know short hand LOL. Plus it could even slow things down more in the thinking department because now you have so many more what if’s… All hands on deck moving units around afterwards could cause a frenzy too (going to need some kind of order).
I know some people do an all axis/all allied turn order, maybe look into that