This letter from Interactive Brokers Group Chairman Thomas Peterffy is illustrative,
https://cointelegraph.com/news/cme-clearing-member-to-regulator-bitcoin-futures-impossible“While the buyer (the long side) of a cryptocurrency futures contract or call option could be required to put up 100 percent of the value to ensure safety, determining the margin requirement for the seller (the short side) is impossible,” he continued.
My commentary: since BTC is a "made up" asset with a finite supply, it is possible that no amount of money could enable a short seller to fulfill a short contract. So there is no reasonable margin rule. The reason is because, unlike everything else traded on the CME, there is no reasonable valuation metric. Stocks and commodities have a long history that enable margin requirements to be set.
Jamie Dimon made the same point. He said BTC has no value, but he would never short it because it could go to $100,000.
So even though there are a lot of BTC bears out there, the only ones who could reasonably short BTC are existing holders of the coin. And without short sellers, there is no futures market. For existing coin holders, short selling is a way to hedge their price, especially if the future price is significantly higher than today.
Also, miners could enter into short selling contracts to sell BTC for a fixed price in 6 months or a year knowing how much they are likely to have.
BTC is about to enter a whole new era.
