how about some kind of application usb stick intigration. so you can use your iphone as a browser
It would make it so you can connect to the usb sticks via blutooth then by selecting a song to play next with your iphone you reorder the tracks inside the appropriate usb stick so the next track when you choose with the cdj will be the one you chose with your iphone.. the good thing about this is you could search on your iphone using additional metadata like bpm, key, comment that isn’t available to older generation technology like cdj1000’s ndx8000 rmp3000 etc… and would really make these devices much more user friendly allowing them to be used for longer inspite of newer technologies becoming available.
Beyond an application like this intigrated with hardware or even software I can’t see much use for an iphone in the booth that will actually be useful, anything you use the microphone for will have too much distortian and/or background noise to operate properly in a loud club environment.
Although maybe you could look into creating a bluetooth network in a venue that can send requests to mobile jocks easily.. just make a really small app that the audiance can download in a couple of seconds to make a request.