It will be great if the app can have the following functions (or in-app purchases):

1) customization/edit tools for styles (and drum fill-in + drum pattern), may be through a step sequencer like interface, so that user can create their own style
2) breaking down styles with drum patterns and and other instrument patterns so that user can mix-and-match the patterns to build up a new style
3) function for user to impose drum fill-in on intended position of a song
4) real-time midi data out (not just exporting song as a midi file, but live streaming midi data out of ios device just like some arppegiator apps are now doing) by using lightening port or wireless midi (network session) built-in in ios+osx so that user can communicate / connect iReal Pro with external sound moudules and DAW