Yeah, "killer app" means a powerful application of technology, not the technology itself. The emphasis is that cool-technology is not enough, you need to get work (or play) out of it.
A warp-drive is just a technology, but "colonizing the galaxy" is the application which will make people really use it.
The thing is, the regular payments system (plastic cards, Dollars, Euros, and other national currencies) already works very well for the vast majority of people. If you're a merchant, then you should certainly think about being able to accept payments in Bitcoin, but as a consumer I'm having difficulty thinking of an instance where I've ever said to myself 'I need some Bitcoin...'. If I was into drugs it would be convenient, I guess, but hte size of the illegal drug market :: regular commerce is pretty small, and I'd imagine drugs about the largest illegal consumer market by a long way. Other contraband markets involve much higher risk factors and are correspondingly smaller.
A warp-drive is just a technology, but "colonizing the galaxy" is the application which will make people really use it.