I'm sorry but I really have trouble believing this. No offense to you at all, but this sounds like something just passed down the rumor mill. DEF systems serve a very specific purpose of reducing NOx emissions, something more unique to diesel engines. If it didn't work, then it wouldn't be on nearly every highway use diesel engine in the U.S. Even VW is going that route on their next diesel. It's not like the EPA told them to use a specific system and they just all threw it on and hoped for the best. The EPA says they must lower emissions of NOx to a certain level and doesn't care how it's done, just that it is done. It if didn't work, these engines wouldn't be certified.I'm a truck driver, been driving tractor-trailers for three yrs now and I've recently heard that DEF run vehicles are showing no proof of improved emissions and very well may stop being used in future diesel manufacturing
That being said, if they can figure out a better (easier/cheaper) way to achieve the same result they may very well stop using DEF systems at some point, but I don't see that happening anytime soon as the EPA regs aren't getting any looser. Mazda claims they will be able to with their new diesel using a lower compression ratio, but last I checked, that engine is delayed and rumors are saying they haven't yet passed U.S. emissions testing.