The Financial Post reports in its Thursday edition that the U.S. Securities and Exchange Commission is expected to approve applications for dual-share-class structures, perhaps as soon as this summer, allowing managers to add an ETF sleeve to an existing mutual fund. A Bloomberg dispatch to the Post says that more than 50 firms, including Blackrock and State Street, are waiting for the regulator's green light to deploy the hybrid structure, made possible after Vanguard Group's exclusive patent expired two years ago. The two-in-one blueprint is a tantalizing prospect for asset managers looking to break into the exchange-traded-funds market at scale, without having to launch a new strategy from scratch. It also offers a lifeline to firms battered by years of mutual-fund outflows, as investors fled for more tax-efficient alternatives. The hybrid structure helped Vanguard save its clients billions in taxes over two decades, but replicating that playbook may prove harder than it looks. Some Wall Street experts caution the shakeup could erode key benefits of the wrapper, especially if hybrid funds face significant withdrawals during market stress. At the heart of the concern is a tax dynamic that ETFs were built to avoid.