I must say that I'm confused by this option.
Tapping on a track already adds it to the current playlist, and typically this swipe behavior is reserved for deleting items.
The option also appears when you swipe to delete an item from the Playing Now list, which doesn't make much sense. (add an item to the playlist, which is already in the playlist?)
But more importantly, it seems to have replaced the swipe from the right edge of the app to quickly bring up the current Now Playing list.
EDIT: I'm an idiot. "Add to playlist" adds to a playlist file, not the current now playing list.
I'd suggest making the pop-up for playlist selection a full-screen view with a cancel button though, rather than a pop-up menu.
Perhaps it's just the smaller size of the 4s screen but it feels very out of place to have a menu look/behave as it does on iOS.