One cool way to handle it would be via a series of short story comics the way Taka does his site.
There could be many incarnations of Gunbaby throughout history.
Blunderbuss Baby, French Musketeer Baby, Blaster Baby, Phaser Baby, etc.
That way we could all make different variations on Gun Baby, and I suspect one sweet anthology...
I've seen the shared world, or theme idea done in fiction. I'm thinking of a series called Sanctuary or Thieve's World from back in the '80s.
http://en.wikipedia.org/wiki/Thieves'_WorldA bunch of authors wrote their stories around this place called Sanctuary. They could use each other's characters, but they couldn't kill them off, etc.
I'm seeing this as looser. Basically each person makes a short story comic that in some way incorporates the idea of Gun Baby. I have an idea for one I would like to do. Of course the great enemy is always time, right? So many cool projects, so little time...