The problem with 'doing things that you can only do on a 3D printer' is that you have locked yourself into a 3D printer.

My plan as a hardware entrepreneur would be to 3D print prototypes and MVPs, maybe even the first production run. Then transition to prototype molds or CNC machining with a lot of setup/teardown. Finally you go with full blown steel molds, dedicated machines, fixtures, etc.

If you design for for only 3D printing, you can't scale past 3D printing.