At least Bitcoin isn't a fractional reserve currency. Bitcoin itself is mined much like Gold and has a limited quantity. The value of each Bitcoin is created and strengthened by the vast quantity of miners around the globe. Bitcoin is a store of value which moves in the direction of the media, government, businesses and developers who support it.
Bitcoin has limited quantity but not the stable value like gold so the chances of using it as reserve for value to any currency is null and bitcoin itself a currency whereas gold is not.
I think the supply we have can still serve many nations, reason being that a time will come that 1 bitcoin will become very expenses, so quantity wont really matter again, but the cost of even purchasing I bitcoin.
If bitcoin supply eventually get exhausted, there will always be chance to transfer within the circulating one, and this is why many people believe that bitcoin has the tendency of increase to about 1 million dollars per one when the supply becomes very scarce and miners can no longer mine again, other than purchasing from already existing holders.
Dont forget the fact too that we still have other good coins too that can serve this purpose, like Ethereum.