PureFL
Also, more vinyl choices (primitives, gradients, etc.). It would add for much more detailed paint jobs and would make painting just a little bit easier for people that have never done it before and want a basic paint job.
I disagree on this point. The vinyl editor is not supposed to make the average gamer a Leonardo da Vinci or a Michelangelo.
All the necessary vinyls are there, and the Forza community has proven that detailed paint jobs can be achieved (and are achieved).
However, vinyl shapes and choices aside, the Vinyl Editor has been made easier to use with features like Layer stacking, custom color blender, and the best feature of all: A canvas. Any Forza painter would remember the "Mini Cooper canvas".
Now, Turn10 has given painters an actual canvas to paint on, and these paints can be saved and later applied to any car in your garage.
Painting video from PAX '09 here:
link