Yes, it would be a stand alone NIS app. People just download it from the app store, enter a delegated key and click start.
There are some problems holding us back though of course. Right now Android only supports Java 6 I think, and we use Java 8. And I guess some problems like that with iOS too.
It of course could be overcome and will be a lot easier I guess after Android supports Java 8, but then again somebody would have to write it.
But in the future, I really do think NEM can be a โharvest on your old mobileโ platform. And if that was so, we could get A LOT of nodes.