I was thinking about this for a while. Why don't we make an app that will be able to scroll through forums talk to people through the app and bring us the newest of osu! News. Just a thought.
I believe that when osu!next will be released, the site will have a mobile interface. And you can chat in-game via your phone using an IRC client such as AndChat (https://osu.ppy.sh/p/irc here for the log in details). Thus, there is no real need for a mobile app.