Wall Street now wants a ticker to hold almost any financial idea an investor might type into a brokerage search bar, from Bitcoin and funds promising two or three times a stock’s daily return to private assets and contracts tied to elections or economic events.

The ETF began as a cheap way to own a broad market portfolio, then became the distribution system for exposures that once required a futures account, a private placement, a crypto exchange, or a patient reading of a structured-note prospectus.

The SEC is reviewing how far that distribution system can stretch. Its June 30 request for public comment covers crypto assets, commodities, heightened gearing, single-stock products, blockchain-based opportunities, private assets, and event…