I think that iTunes won't make a App for Windows 8, however I've imagined how it could be if it existed.
I've used iTunes 11 interface for this concept. The player with controls are in top and top right. You recognize the album mosaic with album names and artists ; when you select an album, instead of show it by a ribbon, the album cover (with a transparency) and the songs' list are at the left. I've naturally used blue color, cause blue is the main color of the album cover (here M83 Hurry Up, We're Dreaming). And the colors change for each album cover, like in iTunes 11. You must imagine it like it was a real app. ^^
I know it seems real, but unfortunately it isn't. But we don't know the things which will exist in the future ...
Hope you like it !