Personally I think this topic is "implemented". What need can there be for a tooltip when you get the option of showing the information in the underlying list.If you want to see the senders address change the relevant setting.
Have you tried the wide or classic views. I have basically no issues displaying my email in those views because I am not trying to fit four columns of information into the width of me screen
Double click collapses all sub folder of the folder double-clicked. So all that is left is for a root folder to be exposed in the folder pane so all accounts can be collapsed. How do you suggest that should be handled in the unified folder view?