It's a design I've been tinkering with for while and have a bunch of notes about. Reputation would be handled by a transparent history of all projects worked on.

The profit-sharing design does not prevent collusion. E.g., if there are a glut of programmers and a shortage of artists in the collective, then two may collude to submit and share a low programmer bid and a high artist bid (and vice versa on another project).

Collectives are hard and are subject to many problems that the free market does not suffer.