It is so perplexing to me that people keep saying "we don't see Bitcoin's killer app yet." This is such a ridiculous statement.
Bitcoin's first killer app is money.
How many new ideas go from a market cap of zero to $4 B in 6 years?!?! Answer: extremely few. If Bitcoin were a startup itself, it would already be well beyond "Unicorn" status.
Of course, the additional applications of Bitcoin and the Blockchain are endless, but it's first killer app is clearly already here, and 4,000,000,000 cash US dollars agree with that.
Of course it's money, those people that are constantly searching for new ways to use the blockchain are underrating it's main use: money. But make no mistake, Bitcoin as in money will take over the world sooner or later, we are on the early days, give it time and it will be clear money was always the #1 use for it.