Oh, that's a really interesting idea. I had thought the slider used a spring of some sort, but apparently it's just freely sliding and the keyway pushes it. You might be able to do that! I haven't worked with dissolvable support material before; that sounds neat. I wonder if it'd be hard to clean out of such a small space?
Either way, they still upped the requirements from "anybody with a Prusa" to "multi-material printer, one of which is dissolvable," which is probably good enough for Medeco to believably claim to buyers that their system is "resistant" to 3D printing.
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.
Either way, they still upped the requirements from "anybody with a Prusa" to "multi-material printer, one of which is dissolvable," which is probably good enough for Medeco to believably claim to buyers that their system is "resistant" to 3D printing.