But V1 & Vr are speeds that on a given day will equate to a position on the runway.
You do not know the actual distance of runway left. (Unless you have some sophisticated performance system).
In any case once you have reached 50' you don't know how much runway you are going to use to put the aircraft back down and come to a safe stop, so know how much runway you have left after Vr is irrelevant.