There's 10 places in the pop-up menu for brushes. There's 10 numbers on most keyboards: They are made for eachother.

Right now there's a couple of view-manipulation tools on the numbers. Here's a vague proposal for where they could go instead:

Brush favourites-cycling to comma and period.

Fit-to-page > Home(?), F12(?)
Fit-to-width > F11(?)
Rotate > semicolon & quote mark
100% > accent (?), F10(?)
Reset rotation > \(?), F9?

Idea 2: 
Put an icon for the 'select favourite presets' in the brush-presets docker. (Discoverability mainly)

Idea 3:
Mypaint has ctrl+number for setting a preset to that number. Could be interesting.

As last, a general reminder that the standard favourite presets need to be discussed.

Reproducible: Always