2017, with bureaucracy an inertia, you can't expect a lot of people to upgrade to it before 2020. So MSC14 should be properly detected. And it is not, because it misses some include paths.

On a sidenote, not related to the beta, Xmlize can be ridiculously slow. Here is are some outputs:

Compilation finished in 0.256 seconds. 0.072 seconds (28.162%) spent on update.
Compilation finished in 0.093 seconds. 0.077 seconds (81.781%) spent on update.