On the desktop app you can sort songs within a playlist A – Z / Newest to Oldest (and vice versa) by Title, Artist, Album, and Date Added: http://prntscr.com/nrhcdh
I would absolutly LOVE a way on the mobile app to—at the very least—allow sorting of songs by Date Added and the ability to display them either old to new and then switch to new to old. I have hundreds of songs saved to many playlists (a couple of which I use almost every single day) and it's super annoying to have to scroll to the very bottom of the list every time I want to lsiten to the newest songs I've added to that playlist.
Updated on 2019-05-22
You can use the filter to change the way a playlist is presented. In songs/artists/albums views, just click the three dot menu to Sort Playlist. Recently added is one of the options. Click it once or twice to toggle between 'old to new' and 'new to old'.