There are plenty of cities and towns that already have a law regarding unrelated tenants. Amherst, for one. Essentially, from what I learned when I was at UMass, the law is enforced in one of 2 way. First, someone (or a few people) gets a PO box and stays off the lease, so nobody can officially say they live there. Second, if fines and/or evictions come, it is after the police have already had reason to enter the house/apartment, be it for liquor or noise violations, drugs, whatever.

In the 2 years that I lived off campus, I was living with 4 other non-related students, a clear violation of Amherst town laws. Other than a tense minute or 2 if the landlord came around, it affected my life not at all. Just like it won't affect most Boston students who do and will live in large numbers for economic and social reasons.