The main stumbling block would be that GM would never let anything other than a Cadillac badge be put on it. They may have put Caddy badges on generic shitheaps in the past, but never another badge on a real Caddy.
When you read about the development history of the VE, it was originally going to be a Caddy wrapped in Holden clothes, but bean counters gradually cut bits out until the final compromise was reached.
At the 2008 Sydney Motor Show, Holden had the Coupe60/Monaro and a Cadillac CTS coupe side by side. After I had finished licking the chrome paint off the Coupe60 and telling the missus that I was going to buy another Monaro, I decided that the Caddy was ugly, too Yank, potentially too expensive in comparison. Oh, how we were encouragingly and naively misled back then.
Yes, today all we can only imagine is a HSV converted 2019 ATS V coupe. Ignoring the unknown cost, could it be a better, more practical choice than the Camaro.