Some mortgage lenders are grumbling about new federal guidelines on nontraditional mortgages issued by bank and thrift regulators late last week, but it’s not clear whether the new rules will force profound changes in the marketplace. The guidance was issued in response to growing concerns those nontraditional loan products – specifically option ARMs and interest-only loans – are being offered increasingly to unsophisticated borrowers who may not be aware of the risks they face if...