1) I don't think this is really a problem? When the walls are open, running stuff is fast. But when the walls are done, the trades come back to make the connect

1) I don't think this is really a problem? When the walls are open, running stuff is fast. But when the walls are done, the trades come back to make the connections, which is slow amd expensive. Or if you messed up and have to fix it when the walls are up. 2) prehung doors help. Drywall is already the cheaper, faster option... but yeah, finish takes a lot of time. Innovations such as giant oversized outlet trims help a little bit. 3) simple rooflines help even when not using prefab, but people seem to prefer complex roofs. Again, asphalt shingles are the cheap option. If you have a single or two surface roof, a roof goes very fast. Where planes intersect is where all the time is. Material costs on a metal roof are still way more than asphalt. 4) most people don't have a somewhere else for the solar to go. Solar tiles are too expensive (materials and labor)... Panels as roof sounds good until you want to have roof penetrations as is normal for plumbing vents, combustion flues, and bathroom ventilation. Gotta make that all mostly waterproof too. 5) framing seems to be getting some labor saving. Prefab sections can save on-site labor. Things like roof trusses fit on a truck nicely. I think I've seen wall segments too, maybe? Stair sections?