Mobile app market is very large and have great potentials. It's a key of success -- without having mobile apps, Uber-like services couldn't succeed.
I saw Ken's mobile wallet uses JS library, and maybe the development was little difficult because he has to import JS into Android Java structure.
But what if we had Java library for Graphene? Anyone can easily subscribe blockchain using websocket, and send transactions without storing their private keys in the server, like current Javascript wallet does. This will bolster Bitshares as a platform.