Add playlist to current playlist

Lately I've been thinking it would be quite handy to be able to add a playlist at the bottom of the current playlist, instead of only being able to replace the current playlist with a new one. Counts for both the Android and web/desktop player.
Comments
Why?
Do you mean nested - how would it appear in the "current" playlist? Or do you mean "append tracks" from a playlist onto the end of the current playlist?
I was thinking about appending the tracks from a playlist to the end of the current playlist mainly.
Although now that you say it, perhaps a "add here" and "add at the end" like the buttons on songs and albums might be nice too.