This idea isn't going to happen. People have talked about such things before and they usually never even get started -like this one. The problem is no central management for the project and no incentive for anyone to produce anything good. Even if it does get started, it will pretty soon lose steam as the stary eyed new developers discover they don't have the inclination to do any more work on the project and decide to go and work on their own thing. Not to mention that the quality of any work submitted is likely to be sub-standard.

Conitec did call for professional animated models about a year or so back and offered to pay for them, but not enough professional quality work was submitted.