The only problem is the word "Concept".
Most recent concepts they have shown us have never translated into production cars. Except for some vague design cues.
The rear angle does remind me of the ATS. And from what we've seen of the ATS Coupe (In spy shots), the general rear shape could be pretty close.
Others say this is closer to what a next generation CTS coupe could look like.
No matter what, it looks great.