The Federal Reserve decided against instituting new mortgage risk weightings in issuing its Basel III final rule this week, a decision that will likely make it easier and cheaper for financial institutions to hold onto their legacy non-agency MBS and thereby reduce the pressure they may feel to deleverage their balance sheets. “In light of new regulations designed to improve the quality of mortgage underwriting as well as continued uncertainty regarding the aggregate impact of pending mortgage-related rulemakings, the draft final rule does not include the proposed risk weights and instead incorporates the risk weights for residential mortgages under the general risk-based capital rules, which assign a risk weight of either 50 percent (for most first-lien exposures) or 100 percent for other residential mortgage exposures,” the Fed said. That means...