If you're thinking of doing something along the lines of 'Wild Cards', whether it's superheroes or not, it's probably not going to work for all of the above reasons and a few dozen more that haven't been stated. As an example...
Let's say you organize this where each player has sole control and copyright over their character, while you get control and copyright over the world at large. Now, how are you going to publish these stories? Online via a game website where revenue is generated through Google Ads or something similar? An official submission to a publishing house? Self publish in e-book or other format?
Next, there's the question of how the stories are written. Are you just cleaning up and editing game logs for publication? Or are the individual players writing stories about their own characters? Will there sometimes be stories about a group of characters and if so, who writes them and how are they written? One individual writes the group story or everyone writes their own character?
Then, there's the matter of payment or revenue sharing. Who gets what and how much? If character A turns out to be more popular and generates more interest/story clicks/whatever, does the owning player get paid more than other players whose characters are involved in stories? That's an express train to apocalypse-level drama on the game.What happens if a player leaves the group through inactivity or a desire to pitch the character on his/her own? How do you split any advances or royalty payments on published books?
There's the pre-printing stuff. You're going to need to pay the writers before publication. If a player agrees to their character appearing in a story they're not writing, you'll have to pay for the character appearance.
How are you going to advertise the stories? Are you going to set up a booth at local conventions to sell copies? Unless you have a publishing deal, that's all coming out of you. You can always set up a 'group trust' that gets paid into, but that opens up more questions and headaches (how much from each story goes into the trust, should there be a 'participation fee' that goes to the trust, will any money you personally put up as seed funding be repaid to you and at what point would the repayment happen)
In short, you're asking for all the headaches of opening and running a MU, along with all the headaches of managing a self-publishing group.