The pencil box for an artist is something singular, the content after a while doesn't change that much, we got our habits, our favorites pens and tools.
Being able to store custom tools, in a drop down list or something, with a feature like "creating a new tool". So we can keep in our Pencil box all our favorites settings like a black feltpen with 100%, 100%, 62% and off beside a white one with other settings, paint brush with paint setted as well etc. etc.
So we can work with our favorites settings for several tools without all the time playing with the knobs.