Proposed regulatory guidance on nontraditional mortgages aimed at federally-insured banks and thrifts could have a ripple effect on the subprime market, an industry trade group has warned. “We think it is likely that the guidance will influence how the secondary market treats nontraditional mortgage products, and that this could result in [it] becoming de facto industry standards,” said the American Financial Services Association in a comment letter on proposed guidance issued by the Federal…