Use boxes / bubbles / balloons representation to make it easier to select, drag, right-click recipients, and allow reorganizing to / cc / bcc recipients using drag and drop in the "Select contacts" dialog, and ideally mail composer window
Very often I want to reorder around who is "to" and who is "cc" in an email thread to direct attention appropriately. Currently (Evolution 3.42.4 and older, and probably newer versions too) it requires precise manual surgery cut-and-pasting, which is not only error-prone, it's also a pain in the butt because oftentimes the list of recipients exceeds the width of the field, you can paste in the wrong place (ex: in the middle of another name/address), etc.
It would be MUCH easier if I could drag & drop people around.
Ideally I'd like to be able to do this directly in the mail composer's to/c.c./b.c.c. TextEntry widgets, but if an intermediary "easy" solution can at least act as a stopgap in the meantime, being able to click the To/CC/BCC buttons to open the "Select contact" dialog and being able to drag & drop between the to/cc/bcc listview widgets, would already be a useful workaround that requires no visual changes to the UI.
Of course, having the full drag and drop reordering functionality right into the mail composer, alongside with the ability to remove a recipient with a little X button next to them, in some sort of balloon/bubble widget like you see in various webmails and other email clients (such as the prior art and "tentative designs" from this old wiki page), would be ideal (as long as you can still copy/cut and paste the whole line if you need to).
Edit: balloons would also make it MUCH easier to have a delimited mouse target to right-click contacts in the to/cc/bcc fields, because right now it's too easy to click slightly above or below them in the textfield and have the completely wrong contextual menu show up