Thanks, from oz! Sounds like the smartest, most nimble and most creative manufacturer would have had their work cut out for them to keep a large mass-market sedan viable in Australia... and, well, ummm... well this IS GM we're talking about here...
But you have to remember: when VE was released, it was
1) late due to GM confiscating development funds causing sacking of most engineering and design staff working on it at the 11th hour.
2) half baked especially in interior, but also the base and large fleet models were underdone mechanically and for refinement (see point 1)
3) then it stultified on the market for nearly four years with no major changes
4) previous models, wagons and utes launched concurrently (at least after 2002) with VE, the wagon buyers waited 18 months, so a lot of off-lease wagons got replaced with other maker's SUVs - similarly, utes went from 20% of VU-VZ 2002-2006 to less than 10% in VE because Ute was AWOl for over two years. Concurrent with low import tariffs and Thai production, you just hand that market to things like the Hilux
5)in VE, Crewman (10% production) and One-Tonner (5%) and Adventra AWD wagon (maybe 5%, badly mismanaged on intro but lots of potential and growing) just disappeared.
6) in 2003-2004 Holden were working on tons of cars for GM North America. At least four (Coupe60, Zeta Impala, Zeta DT7 Cadillac, XT Denali) made it to rolling fibreglass prototype - that is probably about 2/3rds of the R&D budget for each - over $100M. That is the last stage before creating sheetmetal - the fibreglass shell is actualy scanned for the CAD images used for the tooling/presses. Then in 2005 - all cancelled. I suspect Holden saw not one cent of the R&D costs, which would have been in the hundreds of $mill approaching half a $bill.
IOW, the large RWD Aussie sedan is dying because GM (and Ford) decided to kill it, by starving it and mis-steps in planning like Ford's 1997 AU debacle. Toyota has never been able to beat it with the otherwise all-conquering Camry as it did in the US and other markets. Camry has never reliably acheived more than 50% Commodore sales. Toyota is exiting as a manufacturer, having had Detroit do what it could not: kill Falcon and Commodore.
Holden literally had no money to even change the taillights on the VE/WM so it ran from 2006-2013 with unaltered sheetmetal. You cannot do that - it's just too long for your market-leading, money making headliner.
What you saw with VF (and not even all of it) was meant to be released in 2010 as the 2nd gen G8 with improved interior, lightweighting alloy, better DI motors, etc etc etc. I would bet 'Omega' is actually Zeta II.
Holden had DI V8s in 2006 on test/development. I was told this by their senior engine guy. Why not use them? Pure dollars, and GM had decided Zeta was dead.
This is why it's galling to read about how 'unsustainable' Holden is and they 'had to' close it. If GM had left Holden's Middle-East exports alone and given the G8 to Chevrolet instead of landing it to a brand already cancelled the factory would be absolutely firing on all cylinders and be embarrassed for output. GM cored Holden out, then cancelled it's lifelines. Instead of saying, 'these guys know what they're doing, let's help them' they shut it down. 1988-2002 Holden grew to be the biggest maker/importer in Australia. After Lutz declared 'Monaro is the new GTO', GM Vice Presidents reappeared and Hannenberger was ousted, things went pearshaped. How do you turn around No. 1 to No. 4 and halve it's volume in ten years? I don't know, but GM did it.
In the meantime, Holden gave them a knock-the-ball-out-of-the-park Camaro. It's never beat Mustang five years in a row on sales before the current gen. Plus, Mokka/Trax. Plus, things like the Avenir, the Bolt. Cruze hatch. Look under Alpha - you see Zeta-style SLA/multilink suspension.
GM made it unviable, not the conditions. Now the $Au is falling, it will be increasingly more viable especially as an exporter. Just now, GM is starting to realise - they have a real product problem in Australia, and they are killing the evolved solution to it, after putting a bolt through it's nose like a dancing bear.
Even now, it's probably profitable - you just can't justify another car for the plant with such low capacity.