The government has made numerous proposals to get rid of the dollar bill and with the rising cost of metals, the penny (the metal content of a copper penny is actually worth more than 1 cent, the reason why they switched to zinc in 1982). But for whatever reason, it never passes congress. All the surveys, focus groups, and research into this matter using the US public always comes back in favor of keeping the dollar bill and the penny. Even if it is proven beyond a shadow of a doubt with all kinds of models, that the savings incurred by doing just that is a significant one to the US government.
The only way that is going to happen, is that the law passes without regard to what public wants under the guise of "for the good of the public welfare." It wouldn't be the first time something like that passes. I too, would love to see a transition to polymer currency.