The economic reach of Bitcoin is an interesting subject of discussion. In the end there will be a maximum of 21.000.000 BTC. BTC is a eight-digit number.
I suppose that a currency can only be leading if it has the possibility ta pay in small amounts, equivalent tot e.g. dollarcent or eurocent. This statement limits the range of BTC, will the satoshi be the future euro/dollarcent?
In that case the maximum money supply wil be BTC 21.000.000,00000000 is e.g. EUR 99.999.999.999.999,99 (by the way: interesting exchange rate).
The money supply in the Eurozone (M3) is over EUR 10.000.000.000.000
So without any constraints, the structure of the BTC satisfies the necessary condition.
Let's inventory the other constraints.
Bitcoin, as the pioneer currency of them all will surely be able to maintain its position at the top as long as people keeps on believing and patronizing it. Bitcoin has already faced lots of trouble way back and we are all aware of that. It is very necessary that we look back at bitcoin's history so that we may know why and how it was able to stay as the leading cryptocurrency. In terms of being an official currency, bitcoin might have a hard time being on the top since not everyone is knowledgeable about it yet.