FYI, Cummins went the heavy DPF and cooled EGR route so that they could meet the MY2010 emissions standards in 2007... they will be switching their emissions control systems on the next generation of the 6. 7L... . most likely you'll see urea like the MY2011 Dodge 3500/4500/5500 C&C trucks... I wouldn't be the least bit surprised to see compound turbos and some advanced in-cylinder emissions control techniques. Cummins knows what they're doing on the engine design front.
It's still my understanding that part of what is holding the factory power numbers back has more to do with the drivetrain components from the flywheel back than it does the actual engine.
I think you're right about the drivetrain being the limiting factor. Makes me wonder how the Ford is going to handle the 800#/ft. with their little 10-1/2" axle and aluminum driveshaft. One of the reasons Dodge went with the NOX adsorber for 2007 was that the EPA had not given final approval on the use of SCR at that time. They've already gone that way in the CC. As far as the compound turbos go, Ford tried it and we know how that worked out.