A useful feature would be the ability to have more than 1 mirror mode at one time. EX: I work with cubes a lot and if i could mirror X and Z at the same time i would only have to edit 1 corner to edit all 4 of them instead of editing 2 of them. furthermore if i wanted to edit all 8 corners id mirror all 3 at the same time. just a suggestion that would save some people who works with symmetry a lot of time.
Keep up the awesome work on this awesome program.