For me it'd be adding Shrink/Giantess stuff (not the main focus, it would just be in there as a thing that can exist in that universe and we'd see it from time to time- I'd like the idea of it being a rare thing, for example).
Or maybe as a general rule, more "basic game over scenes from losing." Like for example, when I first got to Khulan's floor, and heard she suffocates most of the people who challenged her with her booty, I was totally all like "welp hope she does that to me when I lose to her." So with this general change, that would be an option to happen just from losing to her. Not entirely sure how it'd be implemented without it being RNG based, especially because a large margin of the replayability factor per grill is based upon losing to them and surviving the outcome in order to build some form of a femdom relationship with them. And I definitely like the idea of earning or building slowly up to a bad end. This wouldn't be removing that, but instead adding by default or in general some basic you're-just-a-random-no-one-who-got-defeated endings, based on the first fight with the girl. With each one being the logical conclusion for that specific girl. Going back to the Khulan example, it could be that if she defeats you with a very specific butt attack, then it will auto-lead to the generic bad end of you getting suffocated to death and becoming just another skelly on her floor, for example.
Not sure what I would pick out of these two. Neither of these two would be taking away, only adding. On one hand the giantess/shrink (most likely shrink rather than giantess), while rare, would create a bunch of longer, less shallow content when it was finally explored. On the other, it would be cheaper quick ends, but there would be one for every girl and it would create a sense of anything being able to happen easily and get rid of any plot protection that the main characters has. You can just as easily have the same exact fate as the random fodder who fought that girl before you. There's also the issue of the fact that most of the fodders share the same fate: simply being put behind bars or killed. And some have "long earned, uneasy" fates by default based on the girl's personality. Ie: Scar or Yvonne.
So I'd probably go with the first addition rather than the second now that I think about it.