The concrete 3D printers/extruders I've seen will print a double row about 8" apart, then splooge down a zig-zag between the two creating a wavy interior section to the wall like corrugated cardboard.
Leave it hollow for insulation value, or you could drop rebar down the voids and then fill them pretty easily like an ICF structure for strength. I also imagine that spools that feed out and bend reinforcing steel, post-tension cables, all sorts of things will become possible as the technology is further down the road to commoditization. Or laying in bars, wire or grids manually after the print-nozzle has passed but before the concrete sets would work.
The tech to do this kind of additive manufacturing has been around since the first computer controlled X-Y plotter became a reality. It's just a matter of scale, and of engineering details, with a little materials science thrown in for improving the attributes of the actual materials being printed.
