I admire hugely what engineers have been able to do these last 20 or so years regarding engines emissions and torque/power outputs. This is a bit of an Automotive Watergate moment However, I think this, to a point, reflects on the massive demands being placed on design teams. The goal posts are set higher and higher, there has to be a limit with chat can be done. We are, after all, setting fire to a combustible substance - there's going to be some nasty smelling stuff! This goalpost moving is done with no regard for real-world economies. By that I mean how much does it cost the planet to redesign a whole engine family, run it for a few years, then scrap it and start again.
In a way we're facing an emissions version of Group B rallying... they were just too damn fast and it cost lives. More isn't automatically better. Ask any mechanic about the fragility, the high-stresses, incredible fine tolerances of a modern engine, the two choices if repair - replace an unfeasibly expensive set of parts, or simply bin the engine/car and buy a new one. Insurance writeoff. Send the thing to landfill.

And then we consider the pitfalls of new tech for new tech's sake, diesels filters that clog up if you do that strange act known as driving around town, for one. It feels like we're approaching the elastic limit of what can be done with the Internal Combustion Engine - to the point where they're literally impossible for manufacturers to make them, I suppose.