The killer app is not in what the device is capable of today.
The killer app is not in what we currently imagine the device to be capable of tomorrow.
The killer app will be found in the things we cannot possibly conceive of today, because our pre-conceived mindset hasn't allowed us to adapt to the new landscape.
New categories of hardware don't need a killer app at launch to be successful.
VisiCalc wasn't available day one of the Apple II being released. What was the Macs killer app? Laser Printer? Adobe photoshop? The killer app for the iPod? The dock connector and iTunes for Windows. iPhone? The App Store itself.
You'll want background music while doing whatever it is you're going to do with it.