i think this is a good idea, but it will be abused by the random noobs that like to destroy things. Even if you have to ask the creator for permission, you could save it under your own things and call it your own. To fix that, you should disable the publish part for everyone but the creator.
I know this is Necro but this is really good idea. 1.someone creates save and saves it as public 2.someone else wants to edit it 3.owner gets a message (PM) with two answers accept/decline 4.If owner accepts he can edit it and save it
P.S there will not be any conflicts in saving just editor adds a sign that he is editing
I think, when somebody creates the public save, they can somewhere type the names of the users that can edit it. And when you're looking at the front page or something, it'll show the names of all the users who worked on it. So if multiple people work on one thing, the credit is spread out.