The question with 3D printing is around the materials and the build times. Wood is a great low carbon material, whereas printing in concrete is a different matter.
A low carbon successor to concrete could change this if its low carbon and not so dense that it's difficult to transport (like concrete)
Lego style building recently started to look pretty good. It also has potential of being extremely cheap. It may be even possible to do rearrangements (moving, shortening, enlarging walls etc) later if you feel like or reusing your old house "bricks" to make new one.
This is actually a very good idea. I would personally love an easy reconfiguration that I can pre-design myself: a young kid --> cut off a master bedroom chunk for a semi-detached room; older kid -> his own room, (teen -> full enclosure, enter from the roof :) )
If it is relatively quick/automatic one could reconfigure before/after visiting friends.
For that to be cost effective, I think you would need a pool of other house builders building the same house who need the same parts. Maybe a kickstarter-like project.
Especially if one can source local CnC/machine shops to send material to be pre-cut then delivered on site.
I do see 3D printing eventually being a more efficient way to build spec houses.