I know that people have been less than happy with the Model X's rear view mirror. For those who would prefer not to use half of their screen for the rear view mirror, this kickstarter mirror from Perigon might do the trick. Check the second video on installation, though. Would this setup look too fugly with wire running along the center of the panoramic windshield?
Perigon HD Digital Mirror: Drive safer with no blind spots
Perigon HD Digital Mirror: Drive safer with no blind spots