Killer app would be something which allows you to trade in the exchanges without losing all your coins if they get hacked. That'll bring confidence back to crypto 
I actually wanted to suggest something like an escrow service for cryptos with low fees. But BC already have this BlackHalo so I just suggested that Quote
I cannot see how focussing on allowing a small community to swap funds with each other indefinitely can do much to progress the outwards appearance or long term goals of the effort to bring digital money to everyday people.
Why not? Bitcoin's rapid price rise have attracted investors, speculators and traders. And this rise its value further which also attracted other businesses. And these businesses will bring bitcoin to ordinary people. It's like a chain reaction 
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Almost every coin on every exchange has no need to be on an exchange,
LOL. Imagine only few people are trading and putting their coins on an exchange. The orderbook will be so thin and small buy/sell could fluctuate the market by 50%. You think a businesses would like that?