Diesel engines don't belong in the light duty fleet, whether it is cars or "trucks". Clever of Dodge to introduce one to score the top "mileage" claim in the light duty truck segment, but it isn't worth it in IMO. People in large cities are sick of diesel fumes and smoke and it was clear that had to change decades ago, so that is why emission controls were mandated. The government's approach was to require gasoline and diesel vehicles comparably clean in the light duty segment, so manufacturers have tried to get diesels to comply to gasoline emission standards but with poor results. If you can make diesels clean, then fine, build them. But they can't be any dirtier than gasoline vehicles has been the goal. That approach was in contrast to govenment just outlawing them in the light duty segment.
The hardware that currently exists on today's modern diesels is very complex and expensive, and the software controlling when to regenerate the particulate filter is even more mind boggling and dosing the selective catalytic converter is almost as bad (these reduce nitrogen oxides emissions, not particulate). Temperature extremes, driving patterns, and so much more has to be accounted for reliably for these systems to work well over time and without sacrificing fuel economy. The problem is bad enough for heavy duty vehicles, but for light duty vehicles, it is at least twice as bad, and having a few engineers in Italy thinking they are going to be first to market with one of these contraptions in the light duty segment and have them succeed is ludicrous.
Among all the diesel manufacturers, Cummins has the best diesel emission control engineers in my experience and have the issues in better control than anyone else, and they still have issues that confound them, but far fewer now than in the earlier years. Cold temperatures, short driving cycles, and mostly city driving (light loads) are almost impossible to design for and keep the systems functioning adequately without problems. In the heavy duty segment, though, the driving patterns are usually fairly long, loads on the engine are usually at least moderate and cold starts are less of a burden to design for. So they work a lot better. If you load up a particulate filter too much before you regenerate it (start a fire), the fire will run away and consume the filter internally - developing software that predicts the loading of a filter under a myriad of driving conditions, cold start temperatures and durations, is less than reliable at best and backpressure sensors are also incapable of determining when to regenerate as well. If you start the "fire" too often, then fuel economy suffers and owners get ticked. A really bad design problem to overcome.
As the diesel emission controls develop in the heavy duty segment and become more reliable, then the engine designers can once again design the diesel engines themselves for optimum power and fuel economy and let the emission controls clean up the mess - just as evolved in the long history of emission controls on gasoline engines that started in the late 1960s. That is why today's gasoline engines perform so very well and get robust fuel economy too. But whether such success for diesels in the light duty segment will be achieved under conditions that are not ideal for diesels, I do not expect such good results due to the gunk diesels emit under cold, slow conditions and the severe problem of cleaning it all up.
In the light duty segment, gasoline will decline as the primary fuel as hybrids, then battery electrics gradually displace gasoline completely in new vehicles. But diesel fuel will likely prevail in the heavy duty market for some time. Tesla is foraging into the heavy duty electric vehicle market for city heavy duty needs and may also displace significant portions of the diesel heavy duty city markets, but is not likely to displace diesel for the highway long haul market for the foreseeable future.
