Adapting: I like to adapt the tool head interface and perhaps more of Universal CNC Axis but with other means than smooth rods but for example with alu extrusions as rails.
Experience: I'm not experienced with FreeCAD, but with OpenSCAD: I developed a parametric Prusa-i3 like 3d printer with single length 500mm 2020 alu extrusions in OpenSCAD with wheel carriages on the X and Z axis, and sliders on Y axis, the design is highly modular: https://spiritdude.wordpress.com/3d-printer-ashtar-k/
Illustration: I was not able to extract dimensions from FreeCAD files regarding the UCA (Universal CNC Axis) I saw the "technical" illustration, but it lacked essentials measurements like position of the magnets/insets, polarity of the magnets on tool head vs carriage (imagine the case friends exchanging different tool heads, they have to use the same polarity notions) - can you provide a more technical detailed illustration (a sort of standard of UCA) so others can adapt it? Something like https://e3d-online.dozuki.com/Document/44/.pdf
Precisions/Margins: what are the margins of detach and reattach a 3d printing nozzle to the magnetic carriage, how well does it align as it was before? Are we talking of 1-2mm margins or a magnitude smaller?
Collaboration: I watched various videos of yours you posted on G+, walked through the wiki.opensourceecology.org and I've got interested in UCA, I think there is a potential, once things are well documented, that UCA will be adapted by others, and you get a side-effect of collaboration by having people to improve UCA implementations and provide various use cases (e.g. light, medium or heavy duty application) - so, the position of the magnets and the screws on axis mounts (idler/motor side) to the frame are the core of the definition of the UCA. That's it for short :-)