This is the real problem with the main argument for minting a coin, which is that “yes, it’s a stupid gimmick, but so is the debt ceiling, and the debt ceiling is a lot more harmful than a coin would be”. That’s true, but it’s important to recognize just how damaging the platinum-coin move would be, all the same. It would effectively mark the demise of the three-branch system of government, by allowing the executive branch to simply steamroller the rights and privileges of the legislative branch. Yes, the legislature is behaving like a bunch of utter morons if they think that driving the US government into default is a good idea. But it’s their right to behave like a bunch of utter morons.
It's not happening, but if it did it would be awesome to make it the size of a truck tire.