I don’t think you quite understand inflation. The Supra costs less than it did, the GTR isn’t that different than it was, and the NSX I also similar to what it cost back them.
I can't imagine how difficult this will be. It's already hard enough to do in a 20ish year old E46, much less a brand new car. I wonder if it will even possible to get things like the dash or the air conditioning to work.
Rigidity is not the issue with this platform. The Z4 is literally only a convertible. I am certain there would be no discernible difference in stiffness.
I just looked some more at the pictures. It would seem that 18x11 fronts are not pushing the limits. The fitment is still recessed into the fender quite a bit.
Vote with the wallets, not with the words people. The Chevrolet SS was the enthusiast "dream". V8, stick, four doors, and a sleek (albeit boring) design. Yet they barely sold and it was quickly discontinued.
I will likely try to do wheels, resonator delete (this is common on other B58 cars and I love the sound improvement), and different rear lights if any become available.
The only way I see a viable solution without a second caliper would be to add a way to trigger the rear brakes using the ABS pump/system. The Focus RS has a system like that as an add-on.
I would have to say that it is unlikely this car will be a true drift car without significant modification. It is basically impossible to rewrite the parking brake’s code to lock up on demand. I also doubt there will be a way to decouple the engine from the trans unless someone swaps a manual...