Expanding on the spanking part is something I've been thinking about, actually, and I have some ideas scribbled down to play with once I finish bashing Vanilla's room into shape. (Fixing the dialogue and grammar, toning down or eliminating the "rapeyness" of a couple of scenes, and fixing some game-logic errors.)
I'm not really looking to make it "rough" or "dark", though — certainly not like that "Inner Sanctum" stuff of Aval0nx's, anyway. In fact, it won't even alter the ultimate outcome of the game, as such(*); what I have in mind is mostly just to add some variety to the "cookie stealing" scene by adding a few different paths or scenes depending on whether or not you catch her stealing the cookies, how many times she gets caught, whether you scold or spank her for it, and so on, rather than just repeating the same thing over and over without any effect.
(* in other words, it'd be like the "watersports" scenes; an Easter Egg or "bonus scene" to be found for those who want to see it and actively try to find it, but you would not be required to do so; it won't unlock anything that you need in order to get to the end of the game, or alter the paths you need to take to get there.)