Thomas Peterffy took out a full-page ad in the Wall Street Journal in 2017 warning of the dangers that bitcoin futures posed to capital markets. 

These days, the Hungarian-born billionaire is well versed in cryptospeak. Peterffy, worth $25 billion, said it's prudent to have 2% to 3% of one's personal wealth in cryptocurrencies, just in case fiat currency goes to "hell."

He owns some himself, while his firm Interactive Brokers Group Inc. recently offered customers the ability to trade Bitcoin, Ethereum, Litecoin and Bitcoin Cash, after detecting "urgency" from its clients to get in on the action.