How common is this in worker co-operatives? My guess is "doesn't exist anywhere" -- I'm guessing there's always some correlation between seniority and ownership share, even if it's just "you have to pass a short probationary period before you're an owner".
It sounds like they haven't really thought this through. Besides seniority -- does someone who's worked there for twenty years really deserve the same share of ownership that someone who started last week does? -- there's also hours to consider: does someone who works ten or twenty hours a week deserve the same share as someone who works forty hours a week? I think most would agree that doesn't really make sense, but the current wording of the license mandates it.