I'm glad you like the UI
As far as adding a bag buttons to the start button and the bank window, that's probably not something I'll do.
I try to use the mouse as little as possible. Plus, you can set a key in options to open and close your bags.
Also, once LU19 goes live(probably soon), open/close bags will be bound to the B key and open/close bank bags will be bound to Shift+B. So I feel adding these buttons wouldn't really be advantageous to the UI.