“It feels like a solution in search of a problem,” says Pete Bonnikson, vice president of mortgage operations for E-LOAN, describing the latest product to hit the home mortgage market: The 50-year mortgage. Reportedly the problem this hyperextended loan addresses is affordability for homebuyers in high-cost areas. By stretching the repayment calculation over 50 years, so the argument goes, monthly payments fall by enough that borrowers unable to qualify for any of the other dozens of mortgage options can get a loan. For certified financial planners like Nancy Flint-Budde in Salem, N.Y., it is a tossup as to whether helping...