Since there is no proper solution for this, for fun I created a "poor man's" keyboard navigation for the KM palettes 
Sometimes it is easier to navigate with the arrow keys. Or a simulation of it.
Assumed the palette is vertical.
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A shortcut opens the palette and moves the mouse to the top item of the palette.
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"k" moves the mouse down one item. "j" moves the mouse one item up.
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Enter (or space), triggers the macro and closes the palette.
For example, this macro uses "k" to move the mouse down to the next item in the palette. "27" is (in my case) exactly the distance needed. Of course, this must be adapted to the structure and size of the palette.
It works, but it is what it is 