I think the manufacturers are going to be quiet about the changes for the better they can now do until the garbage stuff is mostly sold, they don't want to get stuck all that junk iron they built to please the EPACAFE is gone.
The changes that have taken place can only be undone through both houses of Congress with a supermajority vote. That isn't likely to happen again in a long long time.
HR4117 will pass sometime this month and cement these changes into law with regards to automotive EPA regs.
It seems to me that most people don't realize yet what's actually happened with regards to automotive emissions standards and the protections that have been put in place to ensure that they are difficult if not impossible to change.
When HR4117 passes, states will be stripped of the authority to do emissions testing as the standards presently don't exist anymore. The states will no longer be allowed to set emissions standards either. CARB is scrambling to stay relevant.
The automotive industry has quickly adapted to changes coming from Washington and there is no reason to expect otherwise when they've been granted freedom and not expensive mandates. Think about it.
But my read of recent events is that your absolutely right, it will be very difficult to bring this level of regulation back with the Chevron standard removal & the congressional requirement restored
I am looking forward to a lot of cheap 22-25 models to buy & delete very soon, some manufacturers might have difficulty reconfiguring for reliability but GM has kept the design close enough to just change out a handful of parts, raise the oil viscosity & let the good times roll again
Except for the Direct Injection, that's still a bad idea that's a bit more involved to replace but it can be made reasonably reliable if the other garbage is gone