(just a quick off-topic note, is the Meta category not for discussion about the Discourse software itself?)
The only forum game I have seen come off as a success would probably be the Destroy the Tower game (well depending on your terms of success, I mean @Swift_Cube couldn’t handle the work in the end but it was fun for everybody and no arguing so pretty close to it), and I think reflecting on that a big part was there being a GM who made the decisions and what he said went. Giving people equal power in a forum game, however democratic, actually seems to be one of the key issues.