I have published a SMT version of the board, ready for PCB assembly to avoid hand soldering a whole heap of resistors and capacitors. It follows my investigations into the cost. You can find the link to the Github repository in the link section.

This version is not tested, as I currently do not have a need for more expanders, as I still have a lot of the THT version, used for example here. However the circuit design is unchanged, only the components have been rearranged on the board, and BoM and CPL files generated for a sample manufacturer, JLCPCB. So it should work, touch wood. I'm publishing it in case someone can use the design.