I'm not gonna put the effort into flags, at least not now, but I just realized this will let me get rid of a bunch of my filters because I can see what I'm looking for at a glance. Mind = blown.
Nice work, Steven! You keep making these feature that I don't realize I need until I have them.
You may be on this already, but things that occurred to me as I was working with them: auto-size columns will need to leave space for icons, and the highlight column should respect alignment settings with regard to icons, too.
Added (again): You know what else would be mind-blowingly awesome? Being able to middle-click on a highlight to filter, just like for other fields. Then the highlighting rules could double as temporary filters.