Since Submaniac recently fixed up a couple of Polyphony's unfinished models, I've found the time to set them up in the game properly.
First, the E36 BMW 323i:
This had some missing reflections, a dodgy exhaust, and bits of bodywork showing through each other, all of which Submaniac fixed. I then edited the badging from 320i to 323i, fixed the rear plate holder being particularly tiny, and equipped it with the optional Style 25 'Classic' 16" wheels that were so common on the mid-range E36. The physics were set up according to a 1998 brochure, and I tweaked the colour choices slightly to match another brochure.
The E36 also appears as an opponent in a couple of relevant places, just to integrate it more neatly into the game.
The other car to return is the Audi A4 Avant:
Submaniac sorted out the lack of reflections on most of the car, then I ported over two colours from the saloon version that the Avant was missing, and replaced a further four to match the saloon (presumably these colours were tweaked for accuracy late in development after the Avant was cut). The physics setup was actually very easy, as the saloon in vanilla GT2 is already using left-over Avant physics, which this mod fixes.
As with the BMW, the A4 Avant shows up as an opponent in the one race series where it's most appropriate, bulking out a relatively short entry list.
With these two in place, pretty much every salvageable and unique car model from the demo versions of the game has now been revived and finished. It also brings the mod right up close to the absolute limits of the amount of content that can be shovelled into the game without crashes. Any remaining cut cars like the Subaru Rex basically don't exist and would need to be created from scratch, and I would rather include content that was originally authored by Polyphony.
There is of course a lot more work to do on the mod outside of this, plenty of bug fixes to add, and there most likely will still be some amount of new content to come, but I'm happy to have reached the milestone of having brought back every car that we can. Cars like the A4 Avant and NSX-R GT1 Turbo were until quite recently thought to be impossible, and so accomplishing this has been a great team effort.
It's on the to-do list.