As of iTunes 12.2 you can now favorite any track in addition to rating it (in iTunes menus, this is called 'Love'). It would be great if the iTunes Mini Player had a keyboard shortcut to favorite/unfavorite the currently playing track as well showing the current status.
Additionally, it would also be fantastic if the mini player could be able access iTunes' 'Up Next' feature. I.e. let me look at what tracks are coming up next in the current playlist without having to switch to iTunes.