Investors who want to bet on Bitcoin may soon have more options to choose from if US regulators soften their opposition to exchange-traded funds tied directly to Bitcoin holdings. Major financial firms including BlackRock, Fidelity and Invesco have submitted applications to sell US “spot” Bitcoin ETFs that would be physically backed by actual Bitcoin. In the past, the US Securities and Exchange Commission has routinely rejected these products, citing wariness over volatility and potential manipulation. Investors took the BlackRock filing, in particular, as a sign that the SEC was close to dropping its longtime opposition to such financial …