All MJ or no MJ

LOOOLL you got it man! Gotta think of the implications 

Technologically that would be fascinating, but I hope not! Filmmakers and the composers of their films' soundtracks spent months, if not years, stressing over and perfecting minor details of the soundtracks for their film and the music that ends up in the film is deliberately chosen to reflect, manipulate and enhance many of the artistic aspects of films. There's so much subtleties to what really is an art form in itself and while I feel an algorithm could possibly find a great fit on the surface (i.e. an uptempo rock track for a car chase scene), it would lack the depth that an deliberately chosen soundtrack could provide. I'm not against fan remixes and editing a scene for fun to see how it would be with a new score underlying it, of course, but I wouldn't be keen for that to become mainstream and automated. 

ALSO to be a smartass:
We already have those. They're called headphones

^ I feel Historic has put more thought into this than Milo.