Here are some features I would like to see in a basic MIDI API intended for a wide range of phones. Not sure if this is already addressed in J2R-234.
MIDI channel - dynamically change volume, or patch number
MIDI file - start, stop, pause, set overall volume, start at a certain position, set tempo, transpose entire song
Generate MIDI data - dynamically build fragments of MIDI data for simple musical excerpts (like a chord) using a programming language, then send the data to the host sequencer for playback. This does not neccessarily need to be a stream of data if that is to CPU demanding.