Not sure if this has been mentioned before (didn't look like it had), but i wonder if it could be possible to put a watch on a particular aircraft on the used market, and to be able to receive email updates when said aircraft gets put on the market?
E.g. if you're looking for a second hand E170, you could put a watch on and receive a notification if one arrives on the market.
To avoid people watching a whole range of aircraft, you could limit how many types are watched and these could expire after a certain period.
Not an essential change, but would be nice if its at all possible to implement and would help with fleet development.