As mixed-income subsidized housing developments reach towns further from Boston, they are encountering a new form of resistance from municipal officials: an argument that the town has satisfied its obligation to provide affordable housing by the mere existence of market-rate housing priced comparably to the subsidized housing developer’s affordable units. This argument has yet to carry the day before the Housing Appeals Committee (HAC) or the Superior Court. But the Supreme Judicial Court has just accepted two cases that raise this issue, one in the rental context and one concerning a home-ownership development.