From a practical point of view you would need a set of very unusual circumstances for the mid point RVR not to be relevant. As the previous poster pointed out you need to prove that the aircraft can decelerate to a safe speed within the first sector for you to be able to continue the approach if the rest are below limits.
From my perspective in the real world on the 737 that means the speed I am comfortable taxiing in CAT 3 conditions, which is pretty slow. Stop end RVR on a lot of CAT 3 runways may not be relevant.
Out of interest are there autoland capable helicopters where this might be an issue or does anybody fly a CAT 3 machine that could do this?