I cant just see how this move will make things easier. As an RO of 3 junior races I am tempetd to just stick with age at 1st of Jan anyway, I think (correct me if I'm wrong) butthis arose out of considerable debate about the issue of older juniors and their progression through longer races to becoming seniors was it right that they could go from 6 mile races one day to any distance the next. I am not sure how this solution serves to address that problem. Initially looking at it its just going to be way more complicated for everyoine concerend from juniors to parents to RO's.
As FJ mentiosn there are notes available but to be honest I think it would be useful if there was a explanation of the rationale for this made here on the forum.