This is why the Apple Watch doesn't need a killer app

This is key. I think these days we basically don't care about a single killer app, partly because we know that if there's a CPU, screen, internet connection and the ability somehow to run software (apps or web apps), the rest will get figured out later by us and by developers. And critically, because of this, the killer app could be different for everybody.

Apple has devoted one of only two buttons on the Watch to communication, suggesting that the company thinks this will be a big reason for buying one; the health tracking stuff will also attract many for sure. But for you it might be neither; for you it might be an app that hasn't been invented yet.