I love Songbird but I was already whether it's possible add an additional column to the Songbird layout, I love categorising my music by dates as well, and find right clicking above the column header to change a little to messy and want even more flexibility.

So here's my mockup of the 4-pane panel library, I think I've made Songbird do this by mistake in the past through a bug. Question is, is this possible?