This sounds to me pretty close to a treasury money market fund, doesn't it? Money market funds are not insured for some nominal amount, but among the most commo

This sounds to me pretty close to a treasury money market fund, doesn't it? Money market funds are not insured for some nominal amount, but among the most common in practice have significant repurchase agreements with The Fed and hold short-dated treasury debt, but this plus your brokerage it's pretty close to the narrow bank idea. I suppose the Fed could try to make the circle slightly rounder here, but they may look at the hundreds of billions of dollars in such funds, which are by nature extremely "narrow" quasi-banking devices (because they only support a tiny form of maturity transformation, in asset type and term length), and decide "good enough, economic needs of this kind met"