Yes it should work on a real CPC464, as it can live completely without the AMSDOS rom. You can of course add it too on the emulated rom board.
However I don't have a CPC464 to test, so I think it would be wisest if the first one I send out, will be to a CPC464 owner, preferably somone who has a MX4 cable/board already.
It'll be free of charge if it doesn't work. I should have parts to make 1 or 2 samples atm.