Well there is a ton of speculation and opinion in there, and I'm not inclined to address all of it, mostly because many of these ideas have been discussed previously on this forum.
But for starters, I think you are under the assumption that diesel tech, specifically the emissions control, has reached a plateau or glass ceiling of sorts. I think we all agree that the current emissions-laden diesels are lacking some of the reliability of older diesels, but we tend to forget that the automobile industry has been through regulatory cycles like this before. In decades past, there were big pushes to make gasoline engines more green: reduce CO2 emissions; use clean (non-lead) fuel; and get better mpg's. Gasoline engines were forced to make leaps and advances to where they are today, where inline 4 turbo's are providing the same performance as 80's era V8's, all while producing less emissions and getting much better mpg. It really wasn't until the 2007-2008 period that diesel engines saw the same sort of regulatory pressure. Not counting the EGR, we've been living with diesel emissions technology for barely 7 years now, and already these newer designs have made improvements in reliability and mpg. Give it time, and I'm sure the engineers and designers will continue to improve and innovate these engines. If there truly was no development potential left with diesel engines, I don't see why big manufacturers would be putting the money and time into developing new diesel offerings outside of the 3/4 ton market (2.8l duramax, 5.0l cummins, 3.0 VM ecodiesel, supposed diesel offerings for Ford mid-sized and full-sized trucks).
European cities have enacted restrictive legislation on diesel vehicles because, for the longest time, there were few, if any, regulations on diesel emissions for most of those countries. The air quality has suffered greatly in those cities as a result. With the regulations as they exist here in North America, I don't foresee the same problem occurring here. Your implication that most of the major diesel engine makers are cheating emissions is based on the actions of a few. So far, the only company that was caught cheating was VW. The EPA has issued a notice of violation for FCA's VM motori Ecodiesel, though so far nothing has been conclusively proven yet. To date, none of the big domestic diesel makers (Cummins, Powerstroke, Duramax) have been charged with anything. You can speculate all you want about how they might be cheating, but that's all it is....speculation.
You're right that there are more options on the table for HD trucks and hauling than there were in years past: CNG, hyrbid gasoline, hybrid diesel, EV. Who knows, 10-20 years from now, HD trucks and commercial vehicles might be powered by something entirely different from what powers them today. However, your claim that gasoline engines are going to take over the HD/commerical market is way off...gasoline engines are never going to be as fuel efficient or as torquey as the other options (including diesel). You can add a few more gears to the transmission and use forced induction, but it's inherently a less efficient and less torquey design. So maybe there are some people who want a gasoline engine for work applications because its cheaper and easier to work on....but when fuel prices go up, and they will eventually go up, those people are going to turn to other options to power their work vehicles.
