If the Bakkt blueprint works as planned, a panoply of new Bitcoin funds would tap the pent-up demand for the cryptocurrency, making it a safe and easy choice for everyday investors—notably millennials getting their first 401(k)s. Wall Street could then tap Bitcoin’s popularity as an alternative to stocks and bonds to generate giant trading volumes. And that flood of institutional buying and selling, in turn, would take the terror out of Bitcoin by smoothing its wild swings in price.

Cracking the 401(k) and IRA market for cryptocurrency would be a huge win for Bakkt. But...