I used to be pretty excited about 3d printed homes, but an argument I've seen, that's made me a lot more skeptical of them, is that much of the work of building isn't putting up the actual walls, it's all the wiring, plumbing, installing windows and climate control and insulation and roofing and whatever else like that that turns a building from essentially an artificial cave into a more livable space. A 3d printer that prints you walls out of concrete or whatever is only doing the easy part for you in that case, and not necessarily even in the most efficient or desirable manner. Not to say that the idea of more efficient ways to build housing cheaply isn't interesting to me, I just think that it'd be something more boring, like a a bunch of improvement to modular prefab construction. 3d printing is an awesome technology, but it's not a good option for everything