Message List:
Moving the status messages up to the top center is a good idea (in the about bar)-- I've noticed I *never* look down there after a month of use-- +has the benefit of a little more screen real estate
Compose:
Good idea hiding the attachment pane unless needed-- also I'd add "drop files here" text-- didn't even know you could do that until I read thru some of the git commits.
-- also maybe simplify/reduce the compose HTML options/icons-- so it only takes one line? who uses that junk :)
-- ugh, move the Send Message to the left!, or change to the grey icons (near spell etc.) -- outlook has it right tho-- (& I don't like outlook)