The subject of the current Museum of Modern Art exhibition "Home Delivery" is historic and contemporary factory-produced housing. The most emblematic object in the show is a model of a prefab house designed in the late 1960s by Richard and Su Rogers. It is emblematic because it is a striking design (a yellow tube of aluminum panels on spindly pink legs), has a trendy name ("Zip-Up Enclosure"), and, while placing second in a competition, was never built. Prefabricated houses have remained an elusive goal for architects, and the MoMA show is a stylish litany of second-place finishers, also-rans, if-onlys, and downright losers. A corner of the exhibit is devoted to a (only slightly rusty) section of the legendary Lustron house, an all-metal 1940s prefab of which 2,500 were built—before its maker declared bankruptcy. Perhaps realizing the somewhat discouraging message of this historical retrospective, Barry Bergdoll, chief curator of architecture and design at the museum, added an arresting fillip: not just photos, models, and drawings of prefabs but also the real thing.