I really think one more variant on warlocks would be refreshing considering all that has been done to nerf them down. As it stands, you have all the natural elements covered except one :water. I would enjoy seeing an ice based damage warlock whose crit freezes an enemy solid (no save). This would be perfect to complement the new teifling race coming out with Sharn. It wouldn't mean another enhancement tree or anything,simply a change of the source of the blast. The deity would be Auril the frostmaiden (naturally).