This is so awesome! I had similar ideas about making custom molds. In particular, if you're building a geodesic dome in particular, have pre-molded edge angles and shapes would be extremely helpful as they are quite complicated and unique
Have you considered doing this for a geodesic dome shape? Also, I always wondered (or was concerned) that having only a small amount of surface exposed to air may cause issues with how the concrete hardens (cracks, variable hardening, ... dunno)... do you see an issues given the small amount of exposed aircrete while drying?