Not a bad idea at all. Most of the stuff in this protocol is already supported by the empeg serial port and would merely need to be translated. In addition to the play/pause/etc functionality, it also lists this:

receive time information of the current song
receive status information Play, Pause, Stop
receive the number of songs in the current playlist
receive the index of the current played song in the current playlist
get artistname
get albumname
get songname
jump to a specific song in the playlist
jump to the mainplaylist

All of that except for the "jump to a specific song" is supported in the serial data with notify=1.

This is not a bad idea at all...