I would very much like to see a feature where you can reinforce areas of the print, like modifying shapes where you can use a different set of settings. More perimeter, denser infill etc.
This can be done today horizontally by using different sets of settings that start and stop at given heights, but not vertically.
For instance, if I make something that will have a pivot point where a centre axel is located to svivel around, I might want to keep the bulk of the svivel arm light weight with lower infill, but very high infill around the svivel point for stabilty.
another use is if I would make a part where I will place a nut inside the print. I might like this portion to be stronger than the surrounding parts, and by having a modifier shape define the area with separate settings, I can easily make this work.