So, I'll just throw some random thoughts here and there and see what you and WanderingEng think.
I know about the whole urea addition thing, thanks to the all of the chatter this has caused over in r/cars on Reddit. BMW and others are willing to use them, Mazda and VW would rather not. Mazda, despite their best efforts, seems to have trouble getting things off the ground. Since VW is cheating, it's no wonder they seemed able to pull something off that Mazda couldn't.
One of the things that has been picking at my noodle since this whole thing was announced, and was talked about a few times over on r/cars, is that car manufacturers allegedly find little ways to cheat on emissions tests all the time. This just happened to be something beyond "fudging with the drive train a bit" and went into a whole new territory. VW knew that this was trouble. Outright. No doubt. No company that big could be that dumb. Here's the thing though, which is crazy, every single diesel car with this system that they bring to the States increases their chances of getting caught. Every single year that goes by that these cars are on the road and being worked on, increases their chances of getting caught. Given enough time and enough cars, it'd probably be inevitable that they'd get caught. So why do it in the first place? Why take such a big risk? It's stupid. It's crazy. It never should have been an option in the first place.
Let's even pretend, for a moment, that the EPA and all the other regulatory agencies would be willing to turn a blind eye to this whole bit, it's still stupid. I mean, look at The Ford C-Max or Hyundai and Kia. Those class action lawsuits were just because the manufacturers decided to fudge the numbers a bit when it comes to MPG ratings. VW? They outright lied. They literally invited the barbarians to their gates with this whole thing and the barbarians happened to have passed the bar exam.