this is speculation, but I think what otting has up his sleeve is none of the 14 proposals that gao report summarizes. the gao report appears to be a sort of rear guard maneuver. otting will say this is what we are doing at fhfa, and we don't need congress. if you want to do something else, call your congressperson and reference whatever proposal in the gao report you prefer.
edit: about the only thing this gao report affirmatively states is that no proposal covers the entire housing finance system (including fha, hud etc). Mnuchin has said for over a year that congressional reform should take a comprehensive approach, covering not just GSEs but all housing finance. so I find this GAO report akin to a "white paper", and you know what happens to white papers...