Currently the fastest way to switch brushes is by the next/previous preset hotkeys (the second fastest way is the pop-up palette/dragging the brush window around to always have it nearby). This has three major limitations:
1. To get to a preset that is more than one preset away requires tapping of the hotkeys.
2. The user must remember their preset setup to utilize this efficiently.
3. Changing the preset order requires changing the pop-up palette, which is cumbersome.

The current best usability example is MyPaint, where the user can assign brushes to number hotkeys with Ctrl+[Number], then quickly switch between them by pressing the number. Additionally, the ability to preserve the color saved with the preset can be toggled. In a workflow that requires lots of brush switching (paint->smudge/blur->paint details->adjust->...) etc. this is, in my opinion, immensely helpful, since the user doesn't need to break his concentration to switch the brushes.  Please add this feature to Krita.

Reproducible: Always

Steps to Reproduce:
Use Krita.

Actual Results:  
No hotkeys.

Expected Results:  
Hotkeys.