There is also the possibility of permanent backwardation of gold/USD. I.E. USD will become so worthless that you won't be able to purchase or sell any amount of gold for any price in USD. Whatever the reported price for USD/GLD, it would be irrelevant. It would be like reporting the price of Seaweed/Diamonds. In this case, however, backwardation of gold/BTC isn't likely. I don't really have enough of a grasp to be able to speculate as to a BTC price of gold. But as a believer in "not putting all my eggs in one basket," I have diversified into precious metals.
Also, a smart bitcoiner will hold some precious metals to spend as cash in the event there is disrupted access to internet or electricity. Bitcoins may become temporarily impossible to spend in both of these scenarios.
I highly question the value of gold and silver in a zombie apocalypse scenario. The items you want to buy are likely to be unavailable for purchase at any price, in which case any form of money is useless.
I question the rejection of easy diversification based on a false choice fallacy.
There is not only one possible iteration of the "zombie apocalypse scenario." It is not either "society is functioning perfectly, in harmony, and the internet/BTC works therefore no need for gold/silver" or "society is completely defunct, absolutely nothing to buy anywhere, internet/BTC
doesn't work in your area, therefore no need for gold/silver." It's not black and white like that. There are a hundred scenarios your best an-cap end-times zealot could dream of that could benefit someone who had a little gold and silver saved, and there are a hundred others that wouldn't. Let's not just pretend only the latter hundred exist.
Also, this:
If you're a bitcoin millionaire then you probably want to be internationally mobile, in which case gold and silver are nearly useless since you can't take them with you across borders.
I don't follow. If we are still talking about your false choice fallacy end-times wet dream where the internet/BTC are spotty/unreliable but conveniently also nothing is for sale at any price, since this is
absolutely the only possible way that an end-times scenario could ever be played out, how do you expect "bitcoin millionare" to be able to buy a plane ticket, and how do you expect airports to be running? And how should he pay the taxi to get to the airport and how should the taxi driver pay for gas? If nothing is available, at any price. I don't know about you but I would offer to pay the taxi driver in silver, then I would find a train willing to take me to another country, and I would offer to pay the engineer in gold. 6000 years of use as a currency does not disappear in a few decades.
Assuming he actually got all those things in a scenario where there is nothing for sale at any price, and assuming the government hasn't placed strict capital controls, even a small bag that is easy to carry traveling could hold enough gold to satisfy day-to-day living expenses for a short while and Bitcoin Supernode would be better off than if he just had bitcoin and no precious metals.