Hello. This thread has snaked around all over the place! Let me try and provide what clarity I can. As people are hopefully currently aware, Extensions do not currently support monetisation. We (Twitch) have said publicly that our next update around monetisation will be made at TwitchCon (which is not too far away now). Extensions that attempted off-site monetisation today are rejected.
That being said, our first foray into monetisation is coming, and soon. There was some healthy conversation in this thread in regards to who will be able to pay for what. I am certain that there will be people who will be surprised by our first foray into Extension monetisation (hopefully in a good way).
My two cents, a gambling Extension would more than likely be ruled out by policy. I do not believe that Twitch wants to deal with the legal ramifications of gambling.