How does one go about that? Create the universe when one first story starts posting, while outlining the premise and the rules of the universe so others can participate, or release the initial story which outlines the story universe's rules, only opening the universe when the initial story is done posting? Or, should I sent out invites to a select group of authors, asking if they're interested and then asking for their input in the universe?
I am guessing there are two parts to this, one part(the Storiesonline side) has been addressed.
The other side appears to be oversight/management/handling of the universe itself. THAT gets complicated, and it can also get messy.
Yes there are examples where it works for the most part(see: The Swarm Cycle) and then there are examples where it can go off the rails in various and sundry ways. Naked in School (Karen Wagner variants) would actually be somewhat of an example. But then, NiS also has the thing where there is no requirement for "external consistency" (between already existing stories) for more than a very small number of bullet points. ....Which is why it can also exemplify how different authors can go different directions even with the same premise and same general set of rules.
Once you start dealing with "a consistent universe" between authors and stories, some kind of gatekeeping starts to become required. Be that a single person, or a group, just also remember that groups can "become political" in some way even if the group politics have nothing to do with the other kind of politics. (Bob always agrees with Sue, Jake almost never agrees with suggestions or ideas from Bob, etc)
The gatekeeping side of things can also get annoying when dealing with variable author productivity and significant events. As it creates scenarios where one author can inadvertently(or deliberately) hold up the work of several others because they're waiting for that author to release a particular story/book first.
And of course, as a universe becomes increasingly large, it becomes increasingly difficult for people to do things without stepping on something. For that matter, many authors have that problem with their own setting. Now try doing that for one with several million written words across multiple authors and a half-dozen or more different story lines.