Wow, this is a great observation. I believe to mitigate the dangers some serious testing needs to be done to see for weak parts and combine that with CNC made metal parts or some other strong material like CF/Kevlar composites or nylon in its critical points. But how would you test its durability? Do you know how they test this 2 million cycles under what conditions (force applied, type of movement)?? It would be great if this could be replicated to test the model. I personally im planning on doing it since im also working with 3D printed prosthetics. Do you know of any international standard to which the design can be subjected to?
I think that testing with overweight and millions of cycles would reveal mechanical weak parts or places where wear resistan materials are needed in combination of stress resistant materials would make this work a great ground breaking base to start with 3D printed and CNC made lower limb prosthetics which are actually useful and affordable.