I think to start with, the risk of information leak is pretty low. There isn't too much motive and we have a pretty legit playerbase that we already trust with other basic rules. There aren't too many people in it for just the victories. But like Gmax said, one person can ruin it for everyone. I think there should be some restrictions on who can see this info and be a spectator, like AG said. There could be a sort of spectators club, with regular players admitted, and any breach of info should warrant blacklisting from all Circus games.
I really like this idea. As someone who has tried to keep up with mafia games, either after death or just out of interest, it is really hard. A lot of times I don't know what happened until postgame, and even then, if the postgame is half assed, I still don't know. This would be a lot of fun to watch, and would help eliminate host-postgame problems. Players just want to know what happened, and a busy or lazy host can be really annoying.