The market is in an amazing bull run, if people want to short the future contract, they gotta own bitcoin first, not a few k, but 50,000 at least to manipulate the market at this point. In addition as I see CME and CBOE only limit 5,000 contract (5,000 BTC) per account, so it is a downside for some1 who wanna short. And the most importantly, the future contract expire in a specific day, so I do not think we need to worry about 10 Dec or 18 Dec, maybe weeks later on expired date.