Hey, that’s me. 
As a new user, coming from Firefox, the first thing I wanted was good keyboard navigation, and was quite disappointed. 
I just posted about it here: Key shortcut to focus on email content?
The Tab key function is a complete mess. I’d be happy if they did two things:
-
Options about what to include in Tab navigation (so we can turn off everything except the panes themselves).
-
Stop the Tab key progressing through the email list. I mean what?! You can use the up/down arrow keys for that, why would the Tab key do that?
Basically if we could reduce the Tab key function to simply cycling between panes (e.g. Sidebar Left, List, Content, Sidebar Right, back to Sidebar Left) that would be awesome. Or simply introduce a “Next Pane” shortcut we can customise. So simple.