Just how unaffordable is the Bay State?. Most Bay State families long ago reconciled themselves to the idea that they'll never live in Boston's most famously posh suburbs — places like Wellesley, Weston, and Duxbury. But the zone of communities whose homes are beyond the reach of all but the most affluent families has expanded with astonishing speed, spreading north and south to absorb historically middle-class towns such as Burlington and Canton. If this trend continues, it raises troubling questions about the future of homeownership for the middle class. … [Boston Globe — Ideas Section]