Run lean, get NOx.It’s been a while - but Honda got snubbed from a different angle in the 80s also. If memory serves, they actually had a carburetor tech that was capable of basically doubling the effective MPG for vehicles back then. i recall reading numbers that were over 60mpg in the typical small, 2000 lb econobox. it was denied for use because the emissions were high per volume of exhaust. The irony was that since it put out so much less exhaust per mile, it was still a gain, but the rulemakers weren’t looking at emissions per mile, they were looking at emissions per volume.
What gets me is that NOx causes ground level smog in the LA basin. So have a car "know" it's there via one of several technologies, behave itself there, and adjust itself for better MPG and CO2 emissions when it's in, say, Nevada.