I have just re-discovered a wish item for GC2's "Civilization Manager" that I wish for GC3.
There are many times when I want to track something specific about the development progress of a particular colony along with what colonies I am trying to track. What I think would be very useful is a column that displayed a note indicator (maybe an alphanumeric character) and the ability to tie the note character to a comment.
For instance, when I type the character "f" into the field for colony Zepher II, a mini-screen would pop up to allow me to enter a short comment, like "watching for completion of research of trade tech". Then if I mouse over the note field for that colony the comment could pop up similar to a tooltip, or clicking on it could bring up the comment in a mini-window. I could have several colonies that I am watching for the same reason and would use the matching note character for all of them. Using one alphanumeric would give a potential of 36 (in English) unique watch reasons (62 if both uppercase and lower case were allowed).
Since I don't know what is in GC3, there may be other places where being able to do something like this would be helpful, but I think the biggest gain would be in the Civilization Manager list.