I'm hoping Cadillac goes back to real names.
Their biggest money maker has a real name, Escalade. That should be a big clue to go back to names.
I would name the CT6 Fleetwood, and the crossovers Deville.
DeVille is the biggest name in Caddy history. The crossovers look similar, so they could be named DeVille 6, 5, 4, etc.
The CTS could be Eldorado or perhaps a new name