Regarding price setting, it turns out that the Chicago Board of Exchange is using the price on the Gemini exchange for their futures contracts:
https://fortune.com/2017/12/12/winklevoss-twins-bitcoin-futures/The Winklevoss twins are co-founders of the Gemini exchange, which Cboe Global Markets Inc. is using as the basis for the daily settlement for the bitcoin futures that began trading this week.
If a whole eco-system is built up which uses Gemini for price-setting, they'll eventually get their ETF approved, also using Gemini for the price.
Actually CME is using
CME CF Bitcoin Reference Rate for daily settlement and
CME CF Bitcoin Real-Time Index for marking to market during the day (basically the same methodology, par some details).
CME CF Bitcoin Reference Rate & CME CF Bitcoin Real-Time Index
CME CF Bitcoin Reference Rate (BRR) and CME CF Bitcoin Real-Time Index (BRTI), a standardized reference rate and spot price index with independent oversight are accelerating the professionalization of bitcoin trading. CME CF Crypto Currencies Indices have been generating BRR and BRTI rates since November 2016 with several bitcoin exchanges and trading platforms providing pricing data, including Bitstamp, Coinbase, Gemini, itBit, and Kraken.
So Gemini is only one of the 5 venue used to compute an average whose value is used to settle the future.