When Michael Piwowar took over as acting chairman of the Securities and Exchange Commission two months ago, he settled on policy goals he might achieve during his limited term running the agency.

The list wasn’t sexy—speeding up the number of days required to settle stock trades, making more SEC filings machine-readable, and revisiting a technical guide for disclosures required of bank holding companies. “We’re at our best when we’re being a boring little regulatory agency,” Mr. Piwowar told an investment adviser conference...