I can see you are native gamblers , even Bitcoins' BIP91 is gonna get a betting, that's amazing and also too hard to predict, I would stay out of this since those 80% miner support must be constant (I think so), difficulty task to discipline and coordinate all the hash power among those. Even if Segwit2x succeed now, the November part will need to have 100% miners support to 2MB block size, tough job.

I think Onehash may add this bet on their site.