I feel like adding all the exclusive cars to the backstage pass should have happened a LONG time ago. The problem with replacing the reward cars in the playlists with backstage passes has been that it has made loads of cars completely unobtainable, as there's never anything available in the AH due to the defective price setting algorithm that doesn't allow people to sell cars for realistic prices. So the cars were taken out of the playlist rotation and replaced with backstage passes, but you couldn't buy those cars with backstage passes.
The other thing they should do is make it so you can buy at least 3 of each car available via the backstage pass. Some cars can be good for multiple classes or types of racing, and you need to have multiple copies as there are scenarios where you can't pick a car and apply a tune, the car has to already be available with the tune you want at the time of picking it.
I just wish I had saved up my backstage passes, as I only have one now. I've bought maybe 20 cars I'm not that bothered about, but when Aug 22 comes around there will be loads of cars available that I'd much rather have than the ones I've already spent the passes on.