I know most people won't agree with me on this, but to me bitcoin will have success as a metacurrency.
What is a metacurrency? Well, as you know, a currency is something that is used as an intermediary to exchange stuffs, right? Then, a metacurrency is something that is used as an intermediary to exchange... currencies.
Are there other metacurrencies? Yes, plenty of them. Gold is the most famous one. We used to buy consumer goods with gold, but we don't do that anymore. You can't buy a pizza or a car with gold. You have to sell your gold against national currencies first. So gold is a metacurrency nowadays. Other fiat currencies were meta currencies in their history. So was the Écu before the euro in Europe, for instance.
That's why I don't care much if my local grocery store doesn't ever accept bitcoins. I'll just buy the lousy money it requests: I'll possess this silly money just the time necessary to buy the stuff I need. A few seconds basicallly.