I'm thinking of working with something like eldritch essences combined with a "stance" type mechanic for some self-buff ability. The basic idea is a lightly-armored, d8 HD, melee class with at-will magical add-ons to their melee attacks for extra damage and/or rider effects combined with at-will self-buff capabilities. Ideally, unlike the Warlock, whatever I call this class wouldn't need to choose whether to gain the buff "invocations" or the essence add-ons, but would gain both in a fitting progression more similar to a martial initiator.
Right now, I'm considering possibly dividing the "invocations" into "disciplines," either five different disciplines or six (Earth, Water, Wind, Fire, Wood, and Metal; or Cold, Electricity, Fire, Light, and Shadow).
Future projects include a new Paladin and Ranger revision, a new Monk revision, and a Ravnica D&D conversion with a base class for each of the ten guilds (Azorius Logistician, Boros Legionnaire, Dimir Secretkeeper, Golgari Graveborne, Gruul Bloodbreaker, Izzet Mathmagican, Orzhov Ghostwayman, Rakdos Hellraiser, Selesnya Convoker, and Simic Visionary).