Good move by the Treasury. Obama adopting the platinum coin approach, in addition to being incredibly unlikely, is also the GOP's best case scenario. That outcome would allow them to engage in an unlimited amount of vapid "fiscal conservative" sloganeering - without ever having to face ire from their own hardcore supporters for backing down, nor having to face the consequences of an actual default. It would also make Obama look foolish in the eyes of public opinion (mainly ill-informed public opinion, but that's beside the point). So, game it one step further - the fact that the platinum coin is the GOP's best case scenario means that the more likely its use seems, the more incentive the GOP has to engage in brinkmanship. Taking it off the table makes the Republicans less inclined to force a showdown.
Mint one a year and start paying off China - "Yeah it's legal tender. We made the Louisiana Purchase with a $10 million dollar farthing"