On another note, UEFA have announced that VAR will be used in World Cup qualifiers from September, despite first three rounds being played without VAR in March. This seems a bit more debatable to me than it being used in some FA Cup games but not others as the games already played have a direct impact on the rest of the competition but the perception seems to be UEFA can do no wrong with VAR and everything about it is terrible in England so I doubt there will be many complaints.
I don't agree with VAR being introduced mid competition, whether that is a UEFA/FIFA competition or a domestic one. It removes the level playing field.