Is it possible to allow keyboard focus in the sidebar, so that we could navigate through folders using arrow keys instead of having to use the mouse?
This is honestly the last major thing that is keeping me from switching from DT2 to DT3 full time.
Thank you for your attention! 
This isn’t possible yet but planned for upcoming releases.
Excellent to hear.
Thanks for both the great product and for your responsiveness to its enthusiastic userbase. 
So pleased to hear that. I am sure that it was doing that with me when I was on my previous machine by the way. My memory might be faulty but when I moved to my new Mac it stopped doing that and I thought something was wrong. That was how I found this page. It would move me one step nearer full keyboard control of what I do on DEVONthink 3. That is my goal. I have some Keyboard Maestro things to aid that already.