I’ve spent quite a bit of time playing with play lists. I’ve also heard from several regularly posters on the forum and seen posts from WD themselves on this. Playlists aren’t supported on the MDL. So although they’ll serve up the standard/default DLNA playlists based on ratings/albums etc…, they wont support custom playlists, even in m3u format. Ie, you can try sticking them in folder and the WD device won’t find them.
The default play lists are available in most DLNA certified players. A good one for iOS is Airplay or Mediaconnect. Both work well, but Airplay is cheaper (slightly more buggy though), and doesn’t need you to spend another few $$ on a codec pack.
Basically, we need WD to add this as a feature for it to work. That and subtitles would be my biggest wish lists. All they need to do is add the ability for it to read m3u files from a folder where the music is, and populate that into their default play lists. Should be easy.
And I remember Tony from WD you said you read all the posts (not sure if true or not), so IMHO all you need to do to get subtitles to work is add the ability to support external or internal idx/sub file support. Airplayer for ipad now supports both, just the server doesn’t.