You end up with bitcoin S&L

Some of the biggest players in the cryptocurrency market are calling for a shake-up in bitcoin futures trading. 

Bitcoin futures started trading on Cboe Global Markets and CME in December and have been steadily growing since, with volumes for both markets at just under 10,000 contracts traded Wednesday, according to data from Bloomberg. At least 30 firms trade on Cboe, according to briefing documents from the exchange.Bitcoin futures are cash-settled futures contracts. At the point of expiration, a trader will receive (or pay out) the difference between the price he or she bought the future at and the settlement price. In contrast, with physical settlement a trader takes ownership of bitcoin at the price established in the futures contract.

OK, if we settle in bitcoin, then why have the fiat at all? 

The futures market, in this case, becomes an S&L pit with bitcoins on custodial deposit and loan. The bit error covered by trader fees.

Welcome to the sandbox, just download the standard  S&L pit, set Coin = Btc and hit go.