Not happening. The new El Camino, G8/Commodore based got axed, and it was much more marketable in the US than a wagon. With Bob Lutz gone no chance, he was the real driving force in bringing the G8 and the Caprice for Police only after he tried to get them to import the G8 every other way and under just about every moniker GM has. Rumor has it, it was supposed to be everything from a new Impala SS, a GMC El Camino, and even a four door Corvette (I don't believe GM is going to do anything with the Corvette other than what it is, front mounted pushrod V8 with a fiberglass/carbon fiber body two-seater, GM will never falter from this setup until sales decline from the price of gas but it was a rumor floating around for awhile sorta like the mid-engine 6 cylinder turbo rumors).
The question is how US manufacturers make determination of what they're going to sell. The low (relative) cost of fuel, up to this point, made it easy for them to build more-costly, less economical to own & operate, SUV's. Are wagons going to come back into vogue at some point? It's anyones guess--if they build it, will the public come (buy)? GM (Chevy) wants to have you consider Equinox & Traverse, or even Tahoe/Suburban to get a wagon fix.
Vehicle certification requirements/costs, crash standards, etc, all come into the mix of what is built and what is not....and with "Government Motors", things like the Volt take precedence, at $41K per copy.
That said, considering that "we" would like to see the Holden Sportwagon become a model available in the US, since the design & engineering has been done, the resistance is probably NOT a matter of whether dealers might like to have it to add to the mix--it's most likely more about the corporate culture and the power of the unions involved. Bringing a GM car in from outside "North America" is a thorny issue. The UAW & CAW certainly aren't friendly to to the idea, regardless of the level of domestic US/NA content of these cars built Down Under.
I really have no idea just how tightly Lutz' hands were tied on the decision(s) about any of the Holden products after GTO & G8, or whether the NA product people at GM (both Lutz and whoever is in charge now) REALLY don't want to have to do the necessary work to give "us" what we want. There are the environmental pressures to be considered, too--even though the relatively small numbers of such cars brought in from Holden probably would not have a serious impact on the CAFE target in the near term. If it was left to Mark Reuss to decide (Google search his name for lots more background), I'd like to think this would be a no-brainer deal, but he's got too many irons in the fire to focus on what could be done with Holden products in NA beyond the Caprice PPV.
What I'd really like to see would be a deal that allowed a selected dealer network to import LHD Holden cars to the US--but most of them go to the Middle East, where emission systems aren't at all like what is required in the US. Either that or establish a system to bring HSV products to the US as LHD models--a bit pricey, unfortunately.