I think cryptocurrency could be a reserve currency in the way gold currently is. Gold does not officially back our currency, but every central bank holds some for several good reasons. It is a store of wealth, it is rare, and it doesn't decay. Bitcoin fits that perfectly.

The only possibility that it will not work as an unofficial reserve currency like gold, is that there is really nothing stopping competitors from creating a better bitcoin. The market will eventually be flooded with all kinds of coins. And which one to hold to ensure the value stays steady? This is the advantage that gold holds, no new element is going to pop up and replace it. All of physics stands against something like that happening.