You could file an issue in the github repository. Complex look&feel changes are not at the top of the list of the devels, but the replacement of an icon might make its way at some point.

Edit, clarification: I am used to a "fixed" order (I should have said a "years old" one) of the sidebar tabs where the identical icons are not a problem. But the order of the tabs is not static; it's customizable by dragging them, and I see how in that case, while rearranging the tabs layout, having differentiated icons would prevent a bit of confusion.