Last year Bitcoin was labeled as the worst investment of 2014, however, bitcoin believers can topple fiat currencies as the widely used mode of payment all over the world. The technology behind it and bitcoin's scarcity can both pose a threat and bitcoin's selling factor. But the question is, can bitcoin really substitute dollar or other currency sometime soon?
Well, it comes down to whether you believe that it will replace regular money anytime soon. I for one don't expect it to replace money at all. It will find a niche and will always have its unique use cases, but it really doesn't need to replace regular money in order to do that. People who expect it to do that may really end up being disappointed.