Responding to the last paragraph, I have seen many attempts to do that kind of thing with wikis and similar done and failed. You can obtain pretty surrealistic stuff, like an exquisite corpse, but not real things. However, that’s not the only pattern in collaborative developing. You can have a main writer, who has a clear agenda, and then people “editing” or “fixing bugs”, or “suggesting enhancements”. And, of course, somebody could be interested enough in pushing the drama in a completely different direction, and fork the novel. It’s actually happened before.
About successful attempts, well, as pointed out above, the novel is finished, I have sold half a dozen copies in Amazon, not that my other novels sell many more, a lot of engagement with readers; I would say it’s successful enough. I have also developed a workflow and tools that I use every day in non-literary projects. And I get interaction from complete strangers, which I guess is all the point of writing :-)
Anyway, thanks a lot for your thoughts.