I have an idea for a proposal. If there is interest, I will write a formal proposal for it. The idea goes like this:
If a player has a guess on what an action taken by another player will be (including a timeframe), they can privately notify all other players. All players (except for the predictor and the predictee) then vote on how many points this prediction is worth (0 through 10). The idea here is that something very easy to predict (e.g. they will post a message containing a vowel) will be worth less points than something very hard to predict (say, the exact text of a proposal.) If the proposal proves true, they announce this publicly (and some number of players state that this prediction did, indeed, happen beforehand). Any person who has made predictions totaling 10 points FOR EACH PLAYER wins the game.