Fannie Mae and SoFi introduced a new loan option last week that lets homeowners take advantage of low rates and use the equity in their home to pay down college loans. Under the Student Loan Payoff ReFi, homeowners can refinance mortgages and cash out while paying down an existing loan balance. Fannie estimates that just 1.8 percent of the cash-out mortgages it finances today are being used to pay off student loans. With cash-out refinances growing, Deutsche Bank said it expects to see refinance activity and mortgage-backed security issuance tick up. The new product is driven by cutting guaranty fees that usually accompany Fannie cash-out mortgages. GSE officials said they received approval...