At the risk of sounding pompous or arrogant, the real answer to this question is strictly a matter of the public knowing diddly squat about how money in general works. 99 our of 100 people simply don't think about it, yet it's a deep subject worthy of many years of study.Those who understand what money actually is, and how it actually works, are all bitcoin proponents already. Bitcoin solves all of the classic problems money ever had and then some, offering exotic new features too. Sadly, money is not a subject taught in most schools, and where it is, students are taught to revere and trust central banks and Keynesian theory that are at the heart of all modern problems with money.If only the world understood just what is in this one 5-minute video, there wouldn't be any other currencies by next week:

Technically currencybitcoin's killer app, but the masses don't understand this yet so failing currency, we are basically just waiting now on a 'must have' application that uses the bitcoin blockchain and no one can live without.The blockchain is such an important discovery in the history of mankind that some scholars are already convinced that it is indeed more important than the internet itself. Afterall, you can lie on the internet... The blockchain, not so much. There are so many theoretical use cases right now it's like we're playing a lottery with one in a million odds; but we have far more than a million tickets!More than likely I'd say that we'll see lots of "quite popular apps" happen simultaneously instead of one really solid "killer app." Some candidate apps coming online now but not popular yet would be: Open Bazaar,, & of course the many regional remittance services. Together they may be enough to take bitcoin all the way to everybody's cellphone... And if bitcoin takes a large enough marketshare away from other currencies, then those will start to weaken and be replaced by bitcoin locally. This is called Hyperbitcoinization and is certain to happen somewhere, and likely everywhere this century.