I experimented with adding numbers to the switchbar buttons a long time ago but it did not quite work out - I think I tried both placing the number before the icon and overlapping the icon and it only made the button look crowded or unclear. Now that I think about it, one option I did not try out was to only show the number when you press the ALT key - I could make it so that the number replaces the icon completely - that would make it clearer. I will add this to my to-do list.
