I mean since I do a lot of visual stuff, and I hardly play season mode/my player mode, from least important to most important, I'd like to:
Find the values where I can change the intensity/positioning of the sun during daylight games across all stadiums
Edit the gamma values so what is black is an actual black color, which would most likely be in the global.iff file along with shader information
Edit animations so that they are sequenced better/smoother (memories of High Heat and their "tune" files...)
Edit all the in-game text, from dialogue boxes, headlines and everything in between.
Theres more but they won't come to mind just yet, and I'm sure a lot of these will take a backseat to a lot of other work