Mutual Interest Media tried to do something like this a couple of years ago. I don’t think their model worked out all that well though, as the site hasn’t been updated in some time. https://www.mutualinterest.coop/

A non-web model that has had some success, and that you might be able to learn from is the Many Worlds Collective, which is a co-op of fiction writers who create stories in a shared universe, and publish anthologies of their authors’ works. https://www.manyworldsforum.com/