Just while we're on the "next Caddy CTS as next Commodore" thing, I just looked up the dimensions of the CTS and it is both longer overall than the VE/VF (+70mm), sits on a very slightly shorter wheelbase (-4mm), and is a fair bit narrower (-66mm). I don't think many Australians would want to buy a longer but narrower Commodore, so for this to work I'd suspect Holden would need to trim about 100-150mm off the length of the CTS.

Some numbers for comparison:

Length/Width/Wheelbase

ATS 4643 / 1805 / 2775
CTS 4966 / 1833 / 2911
VE 4894 / 1899 / 2915