you will almost surely NEVER be able to by a car from btsx .. more likely from bitUSD, or bitEUR ...
You are at least thinking further ahead than most. But I still think you are missing what the future will be.
While shopping, you will tell your phone/computer what you want to price things in, in the near term it may be BitUSD. But you phone will decide what to actually pay with. It will be tied in with AI financial advisers, and it will sell whatever is the best for you, at that moment, find a conversion system, possibly though something like the Ripple network. All the taxes, and everything, will be included and recorded in the deal. An AI networked system will also include coupons, offers to try, and all that also.
But I don't think BitUSD will be used for very long. I predict there will soon be a stable crypto currency that performs much better than USD or any other fiat currency. The USD will continue to inflate (i.e. huge tax on the holders of such), while this new one will do a much better job at recording the value of things over the long term. Anyone got a good name for this one, how about:
* BitStable
* Bit_no_inflation
What does everyone else predict? How would the value of such be maintained/determined? I think something like a canonization process will operate somewhat like the federal reserve. But unlike the federal reserve, who's mandate is to fight inflation AND maximize job growth, BitStable managers will only be worried about no inflation and stable prices.