Looked into transposition and I think it's going to be challenging considering that OnKey doesn't play the music. I have built in a range finder in the new version which picks up your singing range based on your performance and then you can filter songs in your library by your range. Let me know what you think of it.

New version should install on a restart.

Building in a range finder now, and a filter for the songs in your range.

Transposition is difficult if OnKey isn't playing the song itself... maybe if it allows you to play your own mp3s later, then it could be done.