By Siddarth S Feb 3 (Reuters) - U.S. brokerage firms and custodians may seek distribution fees from managers of exchange-traded funds, J.P. Morgan said, marking a ​possible crucial shift in the country's $13.5 trillion ETF market. The U.S. market over the ‌past decade has seen the rise of new fintech firms that introduced commission-free trading, disrupting established Wall ‌Street business models. Platforms such as Robinhood attracted millions of retail investors with zero trading fees and simple mob ...