For Fall 2013, Patagonia is producing a Cap 4 EW One-Piece Suite, a.k.a. a onesie.
Gram counters note that this thing will weigh in at 363 g, 13 g less than the separate cap 4 hoody and bottoms. Yes, it's less flexible but I expect to be wearing this thing around my house pretty much permanently. Unclear whether there is an opening for the buttocks.