[quote=@Roman]
I’ve got something in mind but it’s focused on playing with some Gotham rogues rather than being a Batman sheet concept in itself. If there’s other interest in Batman I have a workable concept for Bat-fam members that I can accomplish the same thing with, but if there’s no Batman at all I can think about taking up the cowl. 
[/quote]

Would be fun to have a Gotham defined by its rogues instead of its Batman. I believe the OP covers it, though, in terms of first-come, first-served in terms of defining a 'franchise, having a player first take ownership of the rogues would be completely acceptable.