Real co-ops have similar structures as you describe. There is a large variety, since their structure often depend on regional regulation, the companies own "constitutional" rules and the legal category they fall onto (worker collectives, client-customer co-ops, co-ops related to banking or credit, agricultural co-ops...).
There's often:
* Minimum ratios of owner workers (never 100%, often more like 30%)
* Maximum difference between lowest and highest salaries (they often have difficulties offering competitive salaries to executives).
* Limits on how much of the profits are reinvested or shared as dividends.
* What happens during crisis times: regulated salary reductions, more executive control...
There can be configurations that can work very well, with a good compromise between worker ownership, openness to investment and global competitiveness.
It's always been niche though. In reality (from personal experience) if the first few founders are able to get minimal capital, it makes much more sense to hire instead of get more co-founders. Even if you can't, it tends to be preferable to keep the founders pool quite small.
Individual shareholder-hires can bring in little capital, have a disproportionate influence on how things are done and are hard to get rid of if things don't work out or if the situation changes (which always does frequently in a startup). There's a reason why this has only been done seriously when workers were desperate to revive an economy, or when they are being exploited by monopolistic corporations. Collective ownership tends to be very hard to organize at the beginning and can be quite inflexible due to the inevitable internal politics. When things are bad, everyone tends to be more aligned towards making things better together. And it only tends to scale when this culture becomes deeply ingrained in the organization.
It can get a bit cultish, Mondragon has their own (rather good) university where they train the type of employees they need (mostly talented hardware engineers, but many other degrees too) and educate them on their culture early. It's just a normal university, you can go anywhere afterwards, but you do end up quite connected to their network in practice.
More info: https://www.nytimes.com/2020/12/29/business/cooperatives-bas...