Is the goal to create a Fantasycraft analog for the 3rd ed warlock? I want to make sure I'm looking at the right book. They were pretty clearly mimicing the World of Warcraft warlock - a lot more direct damage and a lot less variety of casting effects if I recall correctly.
My original inspiration was the Pathfinder Advanced Player's Guide Witch. Over time, it morphed a bit into the 4th Edition D&D Warlock concept. In the end it ended up being a strange mix of the Witch from the APG (Hexes), the 4E Warlock with 4E Familiar rules (it's just a construct, not a real beast or creature, hence why I have no intention of adapting Personal Lieutenant or Animal Partner). I wouldn't mind trying my hand at making a short caster (and I have one with only CoP I-V). The 3E Warlock was a pretty neat idea and they adapted it into two other flavors, if memory serves - a fae version and a celestial version. The default version was an infernal one. 4E then took the concept even farther with Dark, Fey, Infernal, Sorcerer-King, Star, and Vestige flavors. So when I started to change my ideas around, I began to think about maybe having my version of the witch something of a mix of Path and Spellcasting magics. I ultimately rejected the idea, but I can see ways to make it work.
I'm still working on flavorful and tasty Specialties, a Familiar line that isn't Personal Lieutenant in disguise (because I really don't like the idea), and maybe some form of Pact line or series of lines to imitate the different types of Powers-That-Be to bargain with. I'm thinking of using either Alignments or making a variant. There are plenty of generic ideas you can use.