This is a really intriguing system. I'm playing with it and with user TKRoth's train derivative. It will probably take me a while to print and assemble enough to make intelligent comments. However, I offer a big think you for posting the source files on Github so that derivatives can be truly compatible.
I have one question though. Have you considered a KBricks-mini? At 2/3 size the basic modulus would be 16x16 or 2x2 Lego studs. That way it would be very easy to make Lego adapter blocks to add Lego structures to a KBricks creation. if that makes the connectors too small, maybe they could be scaled up a little in relation to the base parts. This would also be considerably faster to print.
Also a thought. How about creating a KBricks group here on Thingiverse (or elsewhere) so that comments and questions could be shared separate from specific model comment threads?