Just because it has been done, doesn't mean it should. Core classes should be general classes in my mind, fit to fill a large range of campaign settings.
This was always the problem with the paladin, its hard to put a paladin and an evil guy in the same party. Yes people have done it, but you have to work to make it work. That's probably why there are now different kinds of paladin's in 4e.
The same should be true for the warlock. Yes, perhaps I want to play the anti-hero I have bad powers but use them for good. Or maybe I just want to have a pact with a good creature and can my powers that way. Why does the warlock need to have a dark taint innately?
Other than that though, I am very excited about the new warlock, it does seem pretty cool.