I think it would be a good idea if, in addition to just a rating, it were possible to leave a short comment on a challenge that you’ve played. There have been so many times when, after playing a challenge, I’ve wanted to give a little feedback on improving the challenge (eg "might need more missile-defence, ") or just congratulations on providing a really fun battle. Things which aren’t really worth opening a thread on this forum (esp. as GSB doesn’t seem to like being alt-tabbed). Comments could be shown in the History panel under an attempt.
Of course, there is a risk that comments could degenerate into “L0lz i beet ur chllenge n00b!!111!” but we’re all better than that, aren’t we?