The US dollar helps to bootstrap the system IMHO, as it is the world's most popular currency, at least for now. The average new user is most likely not going to care about some basket of precious metals or commodities, or even gold.

In fact, if the US dollar does collapse it may give credibility to steem and cryptocurrencies in general as users will see the value of their steem skyrocket alongside the value of their collapsing dollars.

The best case scenario IMO would be a seamless transition from one stable currency to another if necessary. Of course I'm sure that would be easier said than done.