But when in terms of how many mediums, gold is still unknown but bitcoin has a fixed number of 21 million. In order for BTC to be equal the gold reserve bitcoin needs at least have a hundred dollars per coin. Let's see if we can achieved this in a span of 3 years.
The time is changing so does the things around it. We want it or not the time will come that those things that we don't want to accept for example (digital cash, because it's too dangerous or not worth it to some ) will take over and we have no choice but to use it also.
As for bitcoin he is the current king in this digital currencies.