It's pretty easy to make the power, and Cummins already has a 542/1250 marine 6.7. Marines are different but you should see the power curve, it jumps very fast at 1800.
I see even more torque management than we have now, low rpm torque is what breaks things and the power isn't needed at the GCWR in lower gears.
To be honest, I wonder how much is really "needed". At some point the added power just isn't really used.
My truck is making 415/850 to the ground, which is about 490/1000 at the crank. I pull better mileage than a stock truck, with about 1,000lbs more "empty" weight too. Yesterday I pulled a 6% grade at 55 and didn't break 60% load at 19-20K combined. That's not too heavy, but stil not working the truck very hard. I am not sure I meet emissions thou :-)
Emissions will be the biggest PITA with 1000 ft/lbs.
