I see your point - a bit like royalties per print, etc - same dilemma the music / film / tv industries have been facing for the last decade.
But I guess my point is that perhaps there will be 'free' files and 'commissioned' files - and home users / small manufacturers willing to pay to have files created, to in turn mass produce...
Do the designers of tooling for traditional models earn royalties? Or just a once off fee to produce the cad / tooling?