I've seen a concrete 3d printer, but it doesn't look like it would be structural. i.e. not sure how you would print around full lengths of rebar?
Dunno how that sort of construction technique pans out long-term or large-scale but you could get the sort of floorplans the GA generated out of it.
It's a good point that existing architectural concrete 3d printing creates "mass concrete" not reinforced concrete, but mass concrete can be structural.
Lots of Roman stuff is still standing in areas that get earthquakes. The solution is to use a conservative design, with arches and thick walls. Domes are good. We can improve on this with 3D printing, using a structure like mammalian bone: solid near the surface, and spongy in the middle.
The large dome of the (Roman) Pantheon is unreinforced concrete. Most compressive structures built before the modern period (arches, domes, buttresses) were not reinforced with tension elements, just plain masonry.
Dunno what the quality's like, but it's there. It does seem like it would be tricky to scale to structures larger than the practical footprint of their printer, but maybe the thing could be mounted on wheels.
