Need a hint for a printer design

Makes sense. I'm of the belief that 3D printed molds are going to feature more and more heavily in construction/home improvement as printers approach ubiquity. There are so many things that forms and molds are used for that the slightly higher cost of printed molds and forms will be offset by the convenience of printing exactly what you need for a job a few hours or days before you need it, while you're doing another task, instead of buying one. Especially for remote worksites.

As an added advantage, you can print a better/stronger/customized mold/form, instead of just using the same one everyone else buys off the shelf. For a slightly higher cost, they'll be able to ultimately sell the same service at a higher margin because it's "custom".

I visited a mansion in Tennessee which began with imported Italian granite stones... and then at some point, the contractor switched to a system of molded stones involving wooden molds with plexiglass inserts. The resulting stones as molded looked just like the originals and cost a hell of a lot less.

In fact, they suggest that the stones in the Giza pyramid were also cast on site (based upon their makeup and water content).

I've envisioned all sorts of molds. I've seen reproductions of Greek and Mayan columns, glyphs, hieroglyphics... The sky's the limit with respect to SCC as poured into a 3D-printed mold for same.

For a lot of that, I'd imagine you probably don't even need SCC if you use good molding practices. Are you familiar with rotocasting? You could probably rotocast quick setting concrete and then just fill the rest of the mold with either fiber filled or whatever other concrete you need once you have a few surface shell layers in place. You shouldn't have to do too much tamping/vibrating at that point, and it'd be way cheaper/more accessible than SCC seems to be. Of course, wide adoption could also bring down the cost of SCC. I'd still rotocast even SCC, to make sure the surface details are all well-filled, and then fill in the rest of the cavity anyway.

Not rotocasting, but I did two years of rotomolding (plastic) in a huge factory so I can guess the concepts.

They are similar...the primary difference is heat...rotomolding is generally a hot process, rotocasting is generally a cold one.