Imagine your DR Who from the TV show with a time machine. You can go back anytime you want in 4,000 years but you don't know which year. What do you bring as a currency to trade?
But that just means one thing; gold has been around longer.
Like saying that next year will appear NetCoin, it will actually take off and 100 years from now is the regular currency. A person living at such age with a time machine wants to visit our year. He would better bring Bitcoins because Netcoins are yet unknown.