Yaakov: The Fundamentalist Mormons openly practice it in the United States for the last 100+ years without legal issues (as long as it doesn’t involve underage spouses.) Furthermore, Supreme Court precedence from recent years makes clear that the State cannot interfere in such marital/religious rituals.
Interjection: Even if practiced, only a small minority of men and women would actually desire to engage in such marriages, out of both economic considerations and personal preferences, so it is unlikely to cause a reverse Shidduch Crisis. I don’t foresee a groundswell of women signing up to be a second wife, unless they’re part of the Shidduch Crisis of those previously unable to find a husband.