They will get more efficiency out of these engines, it's just a matter of bringing more tools to mass manufacture. For instance, ceramic coating of the pistons isn't a common practice today, yet it is an option for some Cummins engines. If they had a good process for performing the ceramic coating en masse, then that would add efficiency. There's rumors that the next round of HD Pickup Diesels will by and large do-away with the EGR system. This will be driven by heavier use of SCR (which I would rather have, but I won't upgrade my truck for this). There are other DEF delivery technologies out there that show promise, like a cartridge system that only has a heating element, no injector/pump/tank. But we'll see if those ever roll out.
I know that lots of people talk about the added costs of emissions equipment, but I just took a peak at Rock Auto and saw the costs of some of those parts. A DPF for a 2007 to 2012 RAM is 1,300 bucks. Almost the same cost as a catalytic converter for some cars (like high end European cars). Saw the SCR component prices on the newer trucks though and those units are still pricey. But eventually the aftermarket will come on line as soon as those parts require regular upkeep with all the trucks out there and they will get cheaper to some degree. 100 bucks for a DEF injector, 200 bucks for a DEF pump. But then, the common replacement part is typically just the DEF injector. Pumps don't seem to go out as frequently. Ford's prices are within the same ballpark for SCR components. So I'm not too terrified of seeing my truck age. Hope to get 15 to 20 years out if it in all honesty.