I recently did a gig with another DJ who was putting business cards out onto the tables with a QR code on the back that allowed guests to request a song. He also had a screen with the QR code and put up some posters.
Guests could request a song straight into an app - or into his DJ software interface. Being able to integrate that into the queue would be incredible (and then use the filters like genre, BPM, key, year, etc).