For two years, D.C. had had a monopoly on gay marriage on the Eastern seaboard, at least as far north as Connecticut and Massachusetts. Gradually, the city’s exclusive hold on the market weakened, as New York joined the wedding party—-but that’s still not close enough to the city to impact its market share locally.

Now, though, Maryland is coming dangerously close to getting in on the marriage equality scene. After several failed attempts, the House of Delegates passed Governor Martin O’Malley‘s reworked legislation, and a panel sent it to the Senate today. Eventually, it’s expected to come to the voters for a referendum—-and at latest count, half of Maryland supports it.

More marriage equality everywhere is, in my view, an unmitigated good. But just like how Tysons Corner’s adoption of walkable urbanism required some thinking about D.C.’s eroding comparative advantage, it’s worth asking the question: How might the District be affected by citizens of a neighboring state getting the same benefits that before only D.C. could offer?

Marriage, after all, is an economic booster: People spend lots of money getting hitched, and if they have to come here to do it, so much the better. A few months after the District started issuing marriage licenses, Amanda Hess parsed the fiscal impact of gay weddings, and found it to be fairly minor.

That’s not the biggest factor in how marriage equality has bouyed the District, though. Double income, no-kids households are a powerful economic force in gentrifying neighborhoods. The District has long been more desirable for gay folks because of its tolerance and culture—-which has spread beyond just the traditional gayborhood of Dupont Circle—-but I’ve spoken with plenty of people for whom a jurisdiction’s willingness to recognize their equal status with straight people is a real factor when deciding where to live. If they can get that in Maryland, and living in Prince Georges or Montgomery County is cheaper anyway, why would they move here?

Ultimately, I bet more people who live in Maryland already will get married when they might otherwise have just skipped it, with no leakage of same sex matrimonial energy from D.C. at all. But to some extent, it does mean the end of D.C.’s status as an island of tolerance in a sea of inequality. Or at least that the isles of the urban archipelago are growing land bridges.