The price of a Bitcoin broke $4,000 this month. It’s up 400% in 2017, and only two years ago it stood at around $230. With 16.5 million Bitcoins in “circulation,” and the potential for 4.5 million more, the market value of Bitcoin is now a whopping $72 billion. Sister currency Ethereum is worth another $32 billion.

Early Snapchat investor Jeremy Liew thinks Bitcoin will reach $500,000 by 2030. Tech eccentric John McAfee believes it’ll take only three years. That’s $1 trillion of digital coins. Now companies with an idea for...