I don't quite understand the choice of ability scores. Why are attacks dexterity-based? It doesn't seem a key part of the duskblade identity, being super-dextrous. And wisdom? What about a step back to basics? The old 3.5 hexblade - the one I thought we were aiming to update - was Charisma-based. Admittedly, back then any non-studious arcane caster used charisma. But it worked with the hexblade. They ought to be intimidating, so charisma is important. Constitution I definitely get - you're a survivor, and your power comes from taming a curse of ill fortune. As I reflect back on the 3.5 hexblade, what I remeber is the fighting style: you cheat. You left the paladin horrified at how you stabbed someone in the back, to which you respond "only as hard as I could." It feels lacking without a Strength option. So Cha, secondaries Str and Con? Str as a brutal avenger, Con as a valiant defender.
The name Curse Mark needs work. I presume it's a placeholder? How about Mark of Woe? Accursed Mark? Mark of the Accursed. Although it's not standard, I'd be fine with the wording "the target is marked by your Duskblade's Curse."