I find it hard to believe that any form of PoW mining (regardless of algorithm) on a smartphone would ever be popular given battery life considerations.
Why do you think so? My smartphone is on charger almost every night, regularly, and I would be very happy if it would do something useful instead of waiting for the alarm clock to fire up. It's trivial to set preference in any application to work only when the phone is on charger.
Yes I agree mining while charging makes great sense. Given the number of smartphones out there it could represent a huge resource of computing power, possibly larger than computers someday even if only operating for part of the day.