I have playlists in an M3U format. I want to see if I can write a scanner to update playlists on the server from a directory of M3U files.
For general channel development advice, see forums.plex.tv/discussion/comment/1399929/#Comment_1399929.
If you are wanting to access local media hosted by Plex, you would want to refer to the PMS web api documentation.
The IPTV channel shows an example of a Plex channel that pulls the data in an m3u8. His simple version would probably be the best to start - github.com/Cigaras/IPTVLite.bundle/blob/master/Contents/Code/init.py.