If and when the US dollar hyperinflates to the point that the limits are hit it is inevitable there will be a discussion about whether an alternative peg target makes sense. Possibly STEEM itself will be usable as a currency (which would be affect of remaining at the feed limit) at that point but more likely witnesses would agree to feed something else like gold or the basket you describe (perhaps phased in over time). The blockchain doesn't know the difference, whatever value is fed in will be used.
EDIT: See @arhag's top-level reply for more discussion of this.
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.