If they mint it, it will end up being melted down for the metal value in it.
If there were really were enough platinum mined since the beginning of time for the United States to be in possession of one trillion dollars worth of it at current prices, I’d say go ahead — that’s (almost) real money as defined in the Constitution.
But this is pure chicanery at every level, and is yet another example of the abject lawlessness of anybody who wants to pretend that it is in any way a legitimate, moral, and truly legal solution. (Oh, I see that Paul Krugman has given it his blessing. There’s a surprise, huh.) They might as well print it on a piece of paper as pretend that a symbolic 100-oz coin or two is worth a trillion dollars.