Try this scenario out for size:
It is fast becoming obvious to me that Oshawa won't be able to handle all of the Zeta variants that seem bound for production. With that in mind, Holden becomes an obvious source for a few models in limited numbers which might work as the initial way to get some of these cars to market. Long term they won't be able to handle the volume of any Zeta that sells more than 20k/year or so. But what is to stop GM from getting a limited supply of VE based cars sent here as premium models for various GMNA brands while capacity to build more Zetas here is ramped-up? These models could be rotated through with GMNA taking over production of models with real volume potential as capacity allows.
So, say we get a G8/Grand Prix based on the Commodore first and if the demand is there it moves to domestic production at higher volume. Holden then could fill the volume it loses with a Statesman in Buick clothes, and a Ute as a new El Camino. This way, we get what we want more quickly and GM establishes a system to respond rapidly to shifting demand both here and in Australia. The entire range of Zeta/VE cars gets a much wider exposure with the flexibility to shift models and production from market to market as required.
Holden is brilliant when it comes to getting the most out of an architecture. The sheer number of variants it produces from a single basic structure is staggering. This opens up the opportunity for a long parade of niche cars coming to the US in rotation, helping to keep the GMNA lineups fresh over time. Some may stay as niche players while others move to wider domestic production. I believe that VE/Zeta has the potential to be the most important GM car architecture since the "A" and "G" body cars of the past.
Finally, GM has been looking for ways to make the Holden/GMNA connection work for a VERY long time so I doubt you will see a simple, cheap re-badge at all.