I've opened a PR adding this feature and tagged this as release blocker, since I'd like to make sure this is in the beta if Łukasz does not object.

The concerns about the stability of the function I expressed earlier have not changed much, though we did get some feedback from the tz database list that at least make me think that the new approach (excluding posix/, right/ and posixrules) is *probably* the right way to go.