I'm not suggesting, Ken, a DIY recalibration of the RNAV approach only monitoring whether the ice cap has shifted since the approach was created. This wouldn't require specialist equipment and I'm surprised it isn't done.
Surprised? Why? Does "surprise" not reqiure one to assume that it is not done? In fact, scientists routinely measure ice cap movement as part of the research protocols using MUCH better equipment than iPhones and the like. But there is a world of difference between using such equipment for research and using it to update an aviation nav approach. And beyond that, a 50 ft error is within allowables for a non precision approach.