I think this is a really cool idea, but I have a few questions.
You're assuming a working service that someone is already willing to invest in. Where do I get my seed money? Does kickstarter / indiegogo make sense for this?
If the co-op needs to raise a big round can it seek outside investment? Can I take a series A and give one person ("corporations are people my friend") a large pool of shares while also selling shares to my users?
Should the stock be splittable? If I have 500k outstanding shares and my user base grows to 100 million should I split the stock? dilute it?
Should the co-op be able to make a capital call to it's users? ("hey guys, we're going to shut down if you don't give us more cash").
I'm not trying to poke holes. I think this is a really interesting idea (and as startups continue to build communities I think we're going to have to have more outside the box thinking related to how they keep their doors open). I'm sure you've thought about these problems for much longer than I have and I'd love to hear your take on some ways to address issues like that in such a system.