westfw:
the software is difficult to work with, and it isn't simple "plug-n-play". I doubt it ever will be.
As a thought experiment, consider the EAGLE PCB CAD program, which a lot of people try, with a relatively small percentage reaching any level of proficiency. Multiply the complexity by a third dimension. (You can delete the need for electronics knowledge, but add some need for mechanical integrity...)
That's basically what I was getting at. Likely, what we would see would be some kind of "Cricut"-like machine with downloadable designs that could be easily printed out; maybe some kind of sharing as well for those who -can- make designs for those who can't (and/or maybe a monetization system for those who want to sell their designs).
That kind of model (not sure if there is a way to "sell" them online via the site, though) already basically exists for the Makerbot and their "Thingiverse":
...which is a really smart move, honestly. Not everybody has the skills, or can easily acquire them (or have the time to); the problem is that you are ultimately limited to what already exists. Maybe if there were software to allow some degree of customization (I'm imagining something like a gearbox sized in one manner, but such software would allow you to resize it for a different sized motor, or one with a different mounting hole pattern or such) - that could take the designs to another level. If there existed designs based on various standards (like gridbeam, NEMA, etc) for the parts needed - that would go a long way (also, designs that focused on compatibility with stuff like Lego, Vex, and Meccano/Erector, too!).
It would be a nice middle ground between needing full-on 3D design skills vs pre-designed (but "fixed") stuff; thus you could realized many ideas as a maker and be able to implement it from a somewhat off-the-shelf pre-existing designs (modified for your needs).