Another idea for doing this would be to allow user defined smaller icons.
eg: the one I have for high resolution 24/96 flac files
If I have smaller icons for when using 2 or 3 matches (named as HiRes_x2.png / HiRes_x3.png) in my Icon folder, then MB could use those along with the standard colour tags for the other matches.
If the smaller icons don't exist, than MB uses the current default of only showing the large icon for the first match
if you set the max displayed to 2, MB would display icons ending in _x2.png, where they are 8x16 px
if you set the max displayed to 3, MB would display icons ending in _x3.png, where they are 5x16 px
if those named icons are not present for any active rule, only a single 16x16px icon is displayed for the first matching rule - there would need to be an x2 or x3 icon for every rule for this to work
does that match what you were thinking?