How is the playlist data stored? I've done a good bit of work extending the (de facto standard, though undocumented and coexistent with PLS) M3U playlist format. I've figured out how to make it accommodate some nonlinear features, like extending strictly sequenced multimedia (eg. 1. silent photo, then 2. audio track, then 3. audio/video track) into simultaneous multimedia (eg. 1. silent photo + audio track, then 2. audio/video) in the playlist metadata for players that can handle it (including custom players I've made), but which still degrade gracefully into regular sequential "standard" M3U behavior on the existing players.
Playlists are really the playlist itself, the player's support of playback features reflected in the playlist format, and playlist editors. I'm happy to help make LMCE playlists do all that.