This is still in "anyone with a prusa" range, I think. Firstly you can do multi-material on a single extruder head by either changing filament as it prints (wh

This is still in "anyone with a prusa" range, I think. Firstly you can do multi-material on a single extruder head by either changing filament as it prints (which is annoying, but for a high enough target not a problem), or pre-printing a two-material filament; second, Prusa themselves do a multi-filament mod for the Mk3 which can do soluble filaments; third, you might not need a second filament at all: I reckon you could print-in-place a two-part key with a captive pin. You could design in a leaf spring if it needs it. The resolution looks challenging, but you've got to bear in mind that 0.4mm is only the standard nozzle diameter, not the smallest available: 0.1mm nozzles are around and capable of some really fine detail. It's only a matter of time, and probably less than you'd think.