Since you appear to be addressing me directly, allow me to respond to a couple things:
I may have been a tad unclear in my earlier comments. When I say "culture" is the defining part of "witch-ness" in fantasy (other than magic-use), I'm not talking about a cosmetic change. A cosmetic change would be saying (like in Rowling's books), "all magic-users need wands to do magic; without wands they can't cast spells." This would take the place of, say, the restriction that magic-users can't be bound and/or require spell components...that's a cosmetic ("color") change to the way the character works.
"Cultural" means (in terms of a game) tied to the setting in an intimate fashion that affects the system. Even while D&D is "setting-less" in its default form, there are default assumptions one can make based on the systems. Paladins can only be lawful good; acting evil robs them of their abilities. Clerics must act in a certain fashion of lose their spell abilities. Turning undead is tied to being an agent of the divine. The existence of "guilds" (and guild rules) for thieves and assassins. These things define setting. Notice magic-users aren't required to belong to some guild...though that could have been written into the rules (schools of magic, organizations of wizards, etc.).
Consider the Dresden Files setting (which I only know about from having played the FATE RPG at a convention): here you have a wizard society with some fairly strict rules...like not using magic to kill people (in play, our magical investigators had to hunt down a rogue magician that had been using magic "against the rules" - my character ended up shooting her with a gun in order to "stick to the law"). Imagine how such a proscription would change play in D&D! What if wizards were subject to a Law of Three type rule? That's not a "cosmetic" change...that's going to shift system and play in a big way!
The witch culture, in both fiction and "real life" has a lot of ties to womanhood. Kind of. I'm not really sure how to say it...I don't mean feminism or female empowerment (though you see aspects of that), and there are certainly men who practice the craft (in both fiction and reality) but there is something distinctly feminine about it...in a traditional, "this is the female experience" kind of way. Witches share spells the way women (traditionally) share recipes...the Book of Shadows is a lot like a personal cookbook. That's very different from the traditional (and very D&Dish) archetype of wizards being guarded with their secrets, not wanting to share power. Witches work in groups...over and over in fiction and folklore you see this...and they are more potent when doing so. Real witches also involve others in their rituals...ritual magic is very much like performing religious rites, and you get more "oomph" from a bigger participating congregation (just like any church service). There's a sharing of knowledge, and a sharing of wisdom, and a sharing of suffering/experience that is very different from the solitary path of the lonely wizard.
Which may be part of why witches have a history (in fact and fiction) of persecution. They are subversive in a way that wizards aren't. Wizards are weird to normal folks, sure, but they aren't trying to undermine the underlying power structure. They're more likely to use it to make money (getting a job as a "court magician," figuring out how to turn base metal into gold, etc.). Witches are driven out of society (or hide their practice while living within it), because their very culture is subversive. Not because they're "powerful women in a patriarchy" but because of what they embody in the manner in which they work. Helping others, sharing knowledge, helping others to become powerful...these things undermine any power structure by empowering community. Communion with nature, understanding and working with natural forces...these things undermine a (human) culture built mainly on the exploitation of nature and an attempt to master it for human purposes.
The concept of the witch fails, at least in part, due to the structure of the D&D game. Take alignment, for example. Witches can certainly be "good" or "evil" people, but alignment is much more of a "cosmic" concept in D&D (especially AD&D) being based on the whole Law/Chaos struggle of sword & sorcery literature. Which side of the Eternal Struggle are you on? Except in B-horror films (the kind that inspires the "evil NPC witch" found in games like Palladium), most witches have a long history of being on the side of HUMANS (their community, their coven, or - selfishly - themselves)...humans who may be good or evil. On which side of the cosmic struggle are humans? Law? Do witches have to be lawful? What about the wicked crones giving people the evil eye? Shouldn't they be chaotic evil? Does that mean they worship Cthulhu?
Much of witch magic falls into the clerical realm, but (while spiritual) they're not dependent on "the gods" for their magic. Does a witch lose his/her spell-casting ability because she's "on the outs" with the Horned God? No, of course not. But other witches will look at such a practitioner (one who ignores the spiritual component) with disdain and as a rebel who's asking for heavy karma to pay 'em a visit. Similarly, witches don't really fit in the "all things balanced" realm of the D&D druid...they respect nature, they don't work for it. They are humanists (or at least "human centric" or human concerned) first.
The D&D magic-user is much more of a scientist, with the spell research and laboratory thing. You can re-skin it all to be "witchy" making it more of a kitchen/hearth thing, but that's going to call for a restructuring of the rules. Witches don't require thousands of coins to develop spells (especially low-level ones!)...if they did, no archetypal D&D village would be able to support the local wise woman.
The point to all this being you need a system overhaul that really addresses specific setting issues in order to include the witch as a playable character class. At least, if you want to have something that feels "witchy" in the traditional sense. There is very little "witch" to the Hermione Granger character, true enough (though Rowling's overall magic society with its tight community, structured rules, flying broomsticks, and love of potion brewing feels witchy in many ways)...if you wanted, to go that route, you could simply say:
male magic-users are called "wizards," female magic-users are called "witches"
But that would be doing a bit of a disservice to all those male witches out there (not to mention Wiccans!). A similar tact would be in the vein of Bewitched, where the magical society is broken down into "witches" and "warlocks." That's a bit more pulpy (in a kind of Richard Price The Raven way) but it could work. Give everyone find familiar as a starting spell instead of read magic...you don't really need read magic in a witch-based setting (at least not in the current fictional tradition of needing to be "born a witch" to have access to spell-casting).
*sigh* I could go on and on for days on this subject but its 4am my time and I have to get up soon.