Question about the limitations of modding TS4

The simplest answer is no to everything.

With a bit of detail though (the best I can explain at 1 am while being sleepy and without causing confusion): We can't create new animations, tuning, etc. for anything that allows us to travel animated between floors, which are referred to as portals, and we also have zero clue as to how they work. I went over this slightly here when people were asking about converting IL ladders to being functional ladders. So if you are referring to spiral stairs, that won't be possible. If you mean just converting a mesh and making it available as regular stairs, then yes. Brujah has done something similar.

For the bunk beds, beds are super complicated. Like out of every functional object we have this is one of the most confusing and glitchy items to work with due to postures and some other stuff. We also technically have "functional" bunk beds with a "ladder" from one modder, but....it's kinda thrown together and uses a hacky method (and no longer supported last I checked). Any modder could probably slap together a bunk bed like the previous one, but if you want it EA quality and not janky, etc., it's a severe headache that's not really worth the struggle (and technically only 1 person in the community knows how). Besides ladders, spiral stairs, etc. it's a highly requested feature, I would honestly suggest to just be patient and let EA make it like they just did with ladders. Animations are very complicated and why there are so few of us, even less of those who are learning about EA quality.

Other limitations include stuff like not being able to touch 99% of the UI, most of the world data (though a recent simmer might be proving this theory wrong soon), and.....Create new Occult states. And I think touch babies but I have yet to look into them, I'm basing it off the lack of new cribs rather than overrides. Hmmm...can't create walkstyles yet either. I previously would have said VFX but that came out a few months ago. So that's all I can think of at the moment, it usually just depends on the situation and what people come up with, there's some things I haven't seen in a convo yet and whether they are possible or not.

Anyhow, what do you mean a new map mod? Do you mean altering an existing map screen to be something else?