Cores: keep the sneak attack dice and negative amp, but change the +attack portion to +3/6/10 negative spellpower.
Why does Vampire Bite still scale with melee/ranged power on a warlock iconic? Negative or light/alignment spellpower makes more sense, or at least have the option.
Vampiric Blast is....meh? Focused blast is pretty bland and horribly inaccurate on moving targets. Could add in Enervating Shadow, to actually have a useful blast. If you're going to force the warlock out of an aoe blast, at least make the single target accurate.
Also, Lord Vampire form gets +10 spell penetration? That's extremely powerful.