It's good to hear you are open to ideas, but I was really trying to find out if there was anything that you personally wouldn't be comfortable including.
I guess I can just ask about some of the more niche ones here and maybe help set some expectations for what your boundaries are.
Please feel free to give very short and simple answers, especially if one or even all of these suggestions has zero/no possibility of being included. No need to justify it if it's something you aren't comfortable with personally. Everyone has their own boundaries.
1: Male on Male
Would you be open to doing any male on male content? All of the content so far is m on f (with the possibility of Male on futa in the future) so I get the impression this one is a bit of a stretch. Also, if not male/male what about male on Cboy/andromorph (male with a pussy)?
2: Feral bodies
Specifically feral bodied and fully sapient creatures. So like a talking horse/dog/snake etc. To be clear, you would definitely need to be as explicit as possible that these characters are NOT just wild animals so as to avoid entering zoophilia territory. I think this one may be somewhat dangerous with regard to content guidelines, so assuming it's something you're open to, it may need to be rift pack content.
3: Vore
This is a very niche one. Mechanically it may be a bit strange to implement because it would likely take a bit of hand-waving or explanation to justify why your character can survive getting swallowed whole (or shoved into a giant pussy) by monsters repeatedly. Maybe the monsters just get off on predding the mc and just always let him go after they've had their fun. Of course digestion (preferably extremely pleasurable digestion) would also make sense for an enemy that has a game over like the smiler does.
Also, if you are open to vore more generally, would you be opposed to any specific types such as oral vore, anal vore, unbirth or even cock vore for potential male/futa enemies?
4: Transformation
I think transformation could only really work as part of a temporary sequence or a game over. If for example, the mc got TF'd into a furry you would need to go back and redo so much art where he's already drawn as a human, not to mention it would double the amount of work needed for art on any future scenes.
My vague understanding of the lore is that the mc should be fully immune to TF from the nano machines, but there may be extra dimensional sources to justify it. This is especially true if it's only part of a short and fully contained rift contract sequence like the smiler section.
Thank you for keeping up with the comments btw. Oh and sorry for the wall of text, I may have gotten a bit carried away here lol