I agree with Daniel...tax law is very complicated and for the IRS tries to get its hands on as much as possible when there is any sort of USA connection. Was told recently that in France, trading between cryptos doesn't trigger a taxable event, but in USA, even barter transactions can be taxable.I would advise anyone to consult a tax accountant before assuming that you don't need to declare a taxable gain when you buy a car (or anything else) for appreciated bitcoins. Generally, the IRS considers everything to be taxable. Of course, bitcoin, being hard to trace, does make tax evasion a bit easier.
From this (CNBC) website:
So, yes: If you buy a Tesla with bitcoins, the law requires you to declare the gain you made on the coins and pay tax on it. You might get away with failing to report, but you might end up paying the tax plus fees and penalties, and you could go to prison if you cannot convince a court that you acted out of well-intentioned ignorance.
Note also that if you "hodl" forever, you never benefit from your gain.
There is now a poll at Tesla’s Bitcoin Folies – Smart Solutions for those that want to weigh in on Tesla's bitcoin and potential gold purchases.