Depends upon which auto manufacturer. If it's Ford, they never saw an (economic) corner they didn't want to cut. Good enough is good enough in their book. GM can be nearly as "thrifty" on their process. I also worked for them.
For either one of them it needs to be pretty much necessary or an overwhelming improvement at best to pass muster.
I don't work for or sell E3 plugs but found this video below interesting. Does seem to show better economy, but then we're talking stationary engines..... so that'll be the next naysay.
https://www.youtube.com/watch?v=jcVF3xL_fzk