The US Government's Debt Bubble

Many countries are starting to look for alternatives to the US government, partly because of this horrendous debt problem. Is there an alternative that is coming around the corner that might be a solution if that's what they want? I'm sure there is. I don't know what it is and I haven't figured it out. The obvious alternative would be the Chinese currency, but the renminbi is not convertible, not completely convertible yet. So you can't have a world's major currency that's not convertible.