Thanks for the reply. I'm glad you like my efforts. I'm a model railroader, and for the past couple of weeks my hobby time has been primarily going into preparing for an upcoming show. So I haven't played much more with the basic KBricks system.
However, I do have a couple of derivative projects in the works:
1) a car base and negative reserved space piece so that you can cut car models to put the base into them. This is inspired by the Duplo car craze and particularly https://www.thingiverse.com/thing:3220777 which provides a similar cut for creating Duplo cars.
2) some rethinking of 'TKRoth's' train system. Needlepoint axle for low friction (practical powered train??), end beam with separate coupler pocket to allow design of more reasonable coupler, and some other ideas.