When doing reused art scenes, there are several things I usually consider:
First, what is all the art I can use. This includes both parts of existing images, as well as animation poses where the character appears. Sometimes I can adapt one character into another, but that is VERY rare since their body types often don't match up. The image you mentioned is the first one to jump to mind (although it doesn't include Morty in it, so I would need a pose to add him on top (hands and dick and tongue and such touching her is the easy part)). Unfortunately, that is the only one I can instantly think of (there are not many images of Morticia laying in bed), so I would have to do asset review to see if any other shots or parts can fit the situation.
Second, how different can I make the reuse. I try (and who knows how well it works) to make it less obvious that (sexy images at least) are being reused. Standing models I have les off an issue with (and hugs are fine) but hot scenes are another thing. The more similar they are to existing content the less... good I feel they are. I this case, the above image is not the best fit, since it would be shot identical with additions, rather than modifications. Minor, but still important to me.
Third, how much work is the change. Animations tend to be the most tedious, because if I have to make a change, I have to make that change to ever frame of animation. Again, with this image, not an animation so less of an issue. And animations tend not to get reused (because of point #2, try not to be obvious in reuse). But, still, how much do I have to change to adapt it? If I have to redraw every image I use, that is a lot of effort I may not have time for.
At the moment, like many other items in the request list, it is not a priority for me. I have to be in both the right mood and mindset to want to devote the time to a new scene, and right this moment, I can barely motivate myself to draw eyelids...
Also, also, we are closing in on the original promised release of the Unity game, and while that may have slipped back, I don't know for sure. To be safe, I'm not goin to start a new scene of this scale, with major work pending.