Save reminder (little red button that pops up after X minutes of not saving that lets you long press to save… or save and increment?)
saved brush presets presented in a separate slider pallette next to the current brush pallette (in linear mode) or below the list (in grid pallette mode)
quick mockup -
have brushes that work on masks the same way as paint data (smudge mask would be a big one) basically the same way photoshop treats quickmask as just another layer
have the option to shrink / grow masks stronger blur on masks, use some sort of levels filter on a mask…
also small bugfix, double tapping the ipad pencil doesnt alter the sub/add icon (but does alter the function) but you did write it as experimental!