When the people ask about the space in playlist i have seen that the answer isn't simple, so here is my solution, based in later works, only add a simple button to show or hide the songs in an album.
i dont know if that is the solution but i think is very easy to implement, isn't it?
can you see the last album in the pic? the numbers of songs in the album? what do you think about that?
the svg in t download link of course :p