All that bloody Red Bull moaning. Of course they want more freedom in the aero department. That's how the team is build and thats their strong point. aka Newey.
But cost wise, very very expensive and a big waist om money. Aero development can't be transferred or copied to another car as a engine. Teams like Williams, Force India and Sauber, who don't have to invest too much to stay into the midfield, are send way back and the domination of the big budget teams becomes even bigger.
With small envelope of development, an x amount of money would mean a certain gain in laptime, while with lots of freedom, the same amount of money would widen the gap.
You can get a Mercedes or Ferrari engine, and strap it on, but you can't buy a blown diffuser and make it work. You have to develop it on your car.