Soviets were designed as self-governing co-ops - which is similar incentives to a startup with widely held equity right? It's not fully the same of course, but the views aren't so different in their aims.
The closest parallel to an equity structure would probably be to the employee-owned cooperative firms that exist in some jurisdictions. A crucial difference from startups is that equity is not tradable, not available to non-working investors, and cannot be taken with you if you leave the firm. Rather than owning securitized shares, you definitionally are entitled to a share of profits while working at the company; and everyone is entitled to the same share. So, for example, if there are 10,000 employees, you have a 1/10,000 claim on any dividends. If you leave the company, you no longer own shares. And there is no way to buy shares; cooperatives will generally only accept investment on bond or loan-like terms, not equity terms.
Sure, it's not as flexible, especially the totalitarian systems, though co-ops aren't as simply structured in their mature forms.
Look up "Mondragon" for what a modern form of distributist co-ops look like. Not the same share of profits, equity investment is the rule (limited to workers or co-op friendly orgs), and there are many other interesting aspects.