I don't think we need any more bad endings because Thickgravy49 already posted two renders for that: Katie as a hooker and Katie as a stripper.Unfortunately, every time 3Diddly made a poll, most of his patrons voted for the most extreme fantasies. And when you need patron money to pay your bills, you need to make what most of your supporters want. On 3Diddly's defence, he did not included some darker choices but still the manipulation path took a dark turn. I agree with you, most probably the manipulation path would end badly because that was what the patrons wanted.
Maybe it would be better to make 2 manipulation ending; One where Katie resist the manipulation although the experience changes her, she becomes more open and from time to time search for pleasures outside of her home although she still loves Brian. And the other ending will be Katie's falling for Mr Wright and becoming pregnant with her child.
But that means that the 4th ending will be much darker; Katie becoming a drug addicted whore, just like most patrons wanted. I don't like such an ending but it will satisfy a lot of people.
Indeed it might have been that one of the reasons 3diddly abandoned Katie's really was that the patrons favoured (ridiculously) dark endings as they did in Hannah's before and he couldn't follow his own inspirations any more. When he asked for ideas how to end Hannah's I read all these but there was only one I could have liked. If I remember right it was just yours: Hannah carries a child by Orlov while he found another favourite and ignores her. Hannah is very desperate and tries to contact her ex-husband Marc. Finally Marc and Hannah meet but Marc is accompanied by a woman and rejects to take her back. This is a bit of a sad conclusion but may be continued later.