my idea was to let an existing app like djay do the beat matching (which it does really well!) and demixing (less well), and then make a custom app that would a

my idea was to let an existing app like djay do the beat matching (which it does really well!) and demixing (less well), and then make a custom app that would act like a midi controller, adjusting the vocals, beats, melody while songs are transitioning, perhaps working off of cues bookmarked in the songs.