Chances of deleting new vehicles? ZIP,ZERO, NADA. DEF technology is so ingrained into the new trucks it is next to impossible to alter them any more.
As for the fuel economy? The reports I have seen they are no better than my current truck. And at least some of that has come from the crazy rear end ratios manufacturers are installing in new trucks.
My early production 6.7L Cummins dually with a 4.10 rear end gets 10.5-11.5 towing and I have seen as good as 18 highway non towing. Usually at 70 highway I get 17