If I understood the OP properly, the question was at least as much about the roles of Rabbonim in insuring compliance with halachos as it was about tznius standards. And a stark reality is that the roles of Rabbonim in our community are not the same as they were just a few generations ago. The authority to issue piskei halacha has not changed. We are told plenty about ????? ??? ?????. The question is about their responsibility as leaders to set standards and to have some degree of enforcement. Here is where there are huge differences.
1. The Klal does not accept any single individual or group as the benchmark setters to determine what standards should be.
2. The Klal would resent any forms of enforcement, insisting that no one has the right to coerce another to follow a particular standard.
3. Compliance is generally recognized as an individual responsibility, not that of any form of leadership.
4. Nearly any form of enforcement today is (probably accurately) accomplished by punishing the innocent. Example – the yeshiva who will not accept an applicant if the mother drives a car or wears a long shaitel. The child is innocent and is being left to the forces of the street.
Can “Rabbonim” set standards, and can they enforce it? This double barrel question is still unanswered. I doubt there is much disagreement that tznius is a major issue and that there are existing problems.