I like to have a custom buttom on my Cintic 12 WX that acts the same way as the stylus front button: as a panning on/off. This worked well in 2.8. 

Now, when the stylus are in focus of the digitizer it does not turn on panning. Removing the pen from focus and pressing the button, the hand icon appears, and if you keep holding the button and bring the stylus into focus again you will pan, Unfortunatly it does not turn pan of when you let go of the wacom button, but stays in panning mode. Removing the stylus from focus and pressing the wacom button will will turn panning off.

I have tried to assign SPACE-button to the wacom but that does not work at all.

I get along now with the stylus button that works fine, but...