To answer this: I believe that the CT5 will be exactly in between the current ATS and current (third-gen) CTS from a size standpoint.
In other words, I think it will be around 189-190 inches in length on a rear-drive chassis.The car will essentially be what I call a “compact plus” – slightly larger in size than the C-segment (compact) luxury cars such as the Mercedes-Benz C-Class, BMW 3 Series, Audi A4, etc, but priced like those vehicles.
Just a thought regarding revisiting the abandonment of offering a Cadillac coupe. What with COVID 19 affecting so much social behavior perhaps a 2nd look at the coupe market would be in order. Speaking for me I am married, retired no kids and would jump at acquiring a CT5 or CT4 coupe.