It won't get 25 but it will get 20. The urea is the big reason why. The big problem has been the NOX that a diesel engine produces when designed for mileage. Simply the cylinder pressures have to be lower to reduce the NOX to 2012 standards if you don't run urea. You reduce the cylinder pressures and the mileage goes down taking away the advantage of the diesel cycle. You might think you can get around this with a tuner, and you can to some degree by injecting the fuel sooner but your low NOX cam shaft still makes all the mileage rules.
The new Ford can produce more NOX because of the urea injection which converts the NOX to water vapor allowing them to run a better cam shaft for mileage. That's how it was explained to me any way.
There is still regen to deal with the sooting of the Diesel Particulat Filter but only 25 percent as much as the previous generation motor because of the reverse flow exhaust and turbo system on the new engine.