Ability to pin (starred?) messages to the top
As a Fastmail user, I've gotten quite used to "pinning" emails, and then setting my messages list to sort by pinned first. This lets me force important emails to remain at the top of the messages list and is extremely helpful.
I don't see any way to sort the Geary messages list at all yet, but if/when that is added, if there could be an option to "pin" emails to the top, that'd be awesome. Maybe starred emails would be considered "pinned"? Honestly, it'd be best if Geary was able to reflect my Fastmail pins. (If I pin something in Fastmail, then it is starred in Geary, and vice versa.)