It seems there is some interest around the thing.
For Southpaw, there are no rules set yet, we have to make it. Some of us have a five year experience of writing round robin/rpg stories about superheroes of our creation, with an evolution from spoof/humorous style to a more "serious" tone.
The rules I propose are:
1) one main character for each poster
2) no solo stories or spin off allowed. The fictional universe that is the set of the story should be featured only in the story itself, to avoid overcomplication of the universe itself.
About the tone and the theme of the story, I have no preferences. I am interested into superheroes, sci fi, fantasy, alternative history, ancient history... but to say the truth, superheroes stories allow to explore ALL of those themes. About the tone, I must admit I am not really cut for humorous tone, due to "cultural barriers", that means being me living in Italy, I don't get much of American TV, sports, entrtainment (outside of big movie and TV serials), so I usaually miss many jokes and such.
So, yes, I prefer the Vanguard style opposed to the old MBL or JLR.
what I would be really interested into doing is a superheroes series where superheroes begins to appear in our world, and they are the only thing different from our reality. I mean, the world is exactly like our, without any kind of sci fi technology (no teleportation or antigravity, for example) and there are no fictional countrys and such.
