You won't find this in the What’s New document, because technically this isn't a new feature.  We did however spend a significant amount of time reworking the code in Limit Mates to make the functionality more efficient and robust.  Focus was spent on mate flip handling as well as handling the general behavior of components that are linked through both mates within a flexible subassembly, as well as mates at the top-level assembly.

So, while you're testing “Specifying Limit Mate Values in Design Tables” (which is in the What’s New), spend some time testing the limits of Limit Mates in general, which is also a focus area of week 1 of Beta.

-Scott