Bitcoin can be successful but it is just a fact it is not stable enough to have a bright future. It has to prove itself first that it can handle the news of disaster in the market with out wavering just like the other currency do. They do change but not that much to have people loose $100 of dollars if it shift in a heartbeat.
That happens with bitcoin because it is not a currency used widely by users, i agree that the user database if bitcoin is really large but not like fiat currencies, that is the reason why it drops and grows with time because it is not a currency used in big businesses or investments or it is not a currency that is running a lot of countries like dollar.
The users of bitcoin are limited at a moment but that doesn't mean it will be same in future as we will find many new users who will invest their money into it.
there's assurance if many people use bitcoins as a payment method or store accept bitcoins as a payment just which that miracle happens wish for the miners and hopefuly bitcoin will become stable and more realiable so that many people will have interest to use bitcoin for future 