In any case, as long as we’re all spitballing about this, here’s something else to think about. There’s no requirement that a treasury bond be printed on paper. If the government wanted to, I imagine that treasury bonds could be etched onto metal plates. In fact they could be etched onto small, round, metal plates. Round platinum plates, for example.
In other words, I wouldn’t be surprised if you could make a case that a $1 trillion platinum coin is really just a $1 trillion treasury bond. It serves precisely the same purpose, after all. And if Treasury isn’t allowed to deposit a $1 trillion bond at the Fed, why would they be allowed to deposit a $1 trillion coin?