It doesn't need to be heavily moderated to work, it's just about the OP stating the rules of engagement in the thread in the first post...
The thread creator will also expect to personally scrape finalized bets from the different threads cause many users will not report their bets there, not by choice but cause they forgot about the thread at the time when the sidebet was made.
With careful planning and effort from the OP, it can work.
- Jay -
I think you're getting my idea quite in a wrong way, the OP doesn't have to monitor anyone's side bets for them, it's literally going to be an open thread for those who have proposed sidebets to each other on any thread, La Liga, Premier League, BSFL just any thread, having proposed their bets terms and agreement on those thread, the side bets thread would only serve as a thread for documentation, and it's not going to have 50 post in just one or two days because there shouldn't be any form of multiple discussions there, just one party posting the details of their already agreed bet terms, and the opponent quote the post as an indication of accepting the bet, when the bets eventually gets settled, it takes just one of both parties to state that the bet have settled/paid.
Man City are finally have two European titles right, I was actually anxious that the same fate of the shield could end repeating it self, and that would have been such a blow because who knows when next they'll get the chance for another one, but as fate would have it, they were the one who had to come from behind this time around, so they won the penalties, while it was vice versa against Arsenal.
I'm sure every Man City fan or player would pick this victory over that one against Arsenal.