The iOS apps OnSong and unrealbook have this feature (implemented in different ways.) As far as I know, there is nothing that does this on Android currently.
We have it on our list to consider for the future. There would be many things to take into account in implementing it as you are all probably aware.

Slightly related: Apple iOS devices, computers and some android devices often have VGA or HDMI or DVI outputs for TV or projection. Apple TV has Airplay for wireless streaming.