Well urea is not all that complicated. When the light turns on, you add a gallon of the stuff to the special reservoir.
I'm a little skeptical on the 36mpg figure, sounds rather generous.
What I think is one of the problems is that the Wrangler drivetrain would need to be beefed up. A D44 with 400-ftlb of torque and a 2.71:1 transfer case? That's a ridiculous amount of torque!
JP