I don't see the market for this type of car. Couples and Families with money are probably gonna go for an SUV, or a German make. Seems like this car is for a generation that's dying out and not being replaced. People are more casual, these days.
You're right, the market for this type of car isn't very big, but they're discontinuing the MKS this year, which leaves them with only one car and three SUV's.
This car would compete with the Chrysler 300, Charger, Impala, and LaCrosse. So, there is an existing market, but it's shrinking fast, which is a big problem for all three domestic car companies. Large cars were their third pillar of profits right behind Pickups and SUV's. That's why Lincoln made the Town Car for so long. Even though it gave Lincoln the geriatric image, it was very profitable.
GM has made the right decision to completely separate Cadillac from GM's other brands and move the headquarters to New York. One example of why this is an important move is the ATS, which has been a failure. The ATS was originally designed to be the Pontiac G6 replacement. At one point Cadillac offered a four cylinder engine from the Malibu as a base engine. Customers may not know these facts, but they can perceive them.