When you browse the library the header that groups albums under the same album artist is a really nice thing, since it allows you to go quickly move from one artist to the following one.
But when it comes to the now playing list, in my opinion, it doesn't help that much. When you add albums to the now playing list you usually pick albums from different artists: one (perhaps two) from one artist, another one from another artist, and so.
So that could be the look of a now playing list with albums picked:
That is: album artist header - one album - another album artist header - another album... The header is not really grouping here and is taking a nice space in the screen.
I think it would be interesting to have the option to disable it (or to reduce to a horizontal line) in the now playing list.