The financial services industry, braced for what could be its biggest disruption in decades, is about to get an early glimpse at the Federal Reserve's work on a new digital currency.

Treasury Secretary Janet Yellen recently mentioned the idea of creating a so-called digital dollar - a new form of electronic currency that would make the payment system easier for Americans and presumably compete with bitcoin and other cryptocurrencies. But there's little rationale for a government-managed online dollar that looks anything like bitcoin.