I was taking with a friend who said ,"people use Alexa like a toaster, we haven't found what this interface will be really good at" But what if it /is/ just a toaster? Tech people tend to have high hopes for technology but technology must serve a purpose and it will go the way of the dodo if the purpose of not strong or clear. For me, having a voice interface for music and calls is enough justification for such a dev…
I use it for, in this order
* Music
* Kitchen timers while cooking
* Setting simple reminders without having to go into a phone app or some crap (alexa, remind me to do X at 10am)
* Kids asking random questions (alexa, how many moons does jupiter have)
Other random stuff like weather maybe, when a sports game is on...
But this is all just pretty basic stuff you would expect from a voice interface... to me, it has all the "killer apps" built in with the above.