FWIW, farming co-ops are often more similar to the lawyer model, in practice: A small number of owners who hire out lots of manual labor.
You could certainly have a similar model for software co-ops, using contracts for various non-central parts of the work.
Most worker co-ops also include a probationary period for new hires before they become part owners (because to do otherwise would be a bit insane). A really long probationary period with a low chance of conversion starts looking a lot like the lawyer model...