Breaking ranks with many industry groups, Fannie Mae says that proposed guidance on nontraditional mortgage products could provide important standards for the market and improve secondary market execution, at least from its perspective, for products such as option ARMs and interest-only loans. At issue is guidance floated by federal bank, thrift, and credit union regulators, which would establish new standards for the underwriting, marketing, and sale of exotic loan products. Regulators have argued that…