I am thinking it would be useful to allow for something like special threads, since we already do have those.
Among others, I am referring to a long-standing (more than 10 years) thread on /g, that allows scat:
https://boards.guro.cx/g/koko.php?res=23522
Another one, younger:
https://boards.guro.cx/g/koko.php?res=127700

It all depends on the main focus of the thread. Is it about pee/scat, or are those just adding to the story?
death naturally often comes accompanied by emptying of bladder/bowels, so it can make sense without being about pee/scat

There is already another important distinction as of now: /s does not have to be gore. (!)

galathien has a point about watersports. most people seem not to mind pee, or even like it, while the majority
strongly dislikes scat and probably vomit. Still I don't think that there is need for a dedicated board for pee,
since you can create a thread on /s and explicitly exclude scat/vomit. If you set your bookmarks accordingly, you
can have an exclusive watersports thread on /s, without ever having to look at scat.

As for discovery of such a thread, you can always link from one of your other threads directly to it.
("hey, look I made something about pee") and be very specific about what goes there.
e.g. loli forced piss drinking ONLY! or something like that.
There are already dedicated threads about watersports alone on /s, as well as AI threads.

To the suggested boards:
people feel strongly about scat and people feel strongly about AI.
I think a poll is a very good idea.

My own opinion is this:

>- A new board for AI-generated Scat/Urination/Vomit content
this opens up a whole new can of worms. what about /fur and /f? dedicated AI boards for both?
that seems like overkill. anything else seems unfair.

>- AI-generated Scat/Urination/Vomit going to /ai/
here you got the problem mentioned above: /s does not have to contain guro, it is dedicated to scat and such.
this would make AI a new top-tier entry, where anything goes, as long as it is AI.
again: what about /fur and /f (AI)?
This would make sense, if the dislike of AI among most users is strong enough to completely ban anything AI to its own area.
I don't think it is that strong, but I may be wrong.

>- AI-generated Scat/Urination/Vomit going to /s/
as it is lived and practiced right now and it works well, imo. I would leave it at that, but:

modify the existing rules a tiny bit to make room for outliers.
the rules already state, that you MUST enter the subject of a new thread.
You can already exclude stuff by being very specific. Why not make room for including stuff?

With 1) a warning:
e.g.: "This special thread alone may include pee or scat, art-style AI/3d also welcome..."
and 2) an explanation
"pee and poop only while dying, (not alone!)"

thus legitimizing a lot of already existing "illegal" threads after the fact, that have often been tolerated for a long time.
the rules should reflect the way, the board is filled with life.

To summarize:
1) dedicated stuff should go to its own board. If it is about scat, fur and so on it has to go there, but it does not have to contain gore.
2) AI is never about AI (*), so it should be judged by content, or ALL AI of any kind would have to go to a single board, which in turn would not have to contain guro.
3) Explicit rules about how and why exceptions can be made would be nice.

Changes necessary for #3 would be minuscule and would have the great benefit of silencing a whole lot of discussions and confusion once and for all.

(*) AI is an artistic style, or method of creation, like drawing, cgi or even text for that matter, while gore, scat, pee, fur and freaky stuff are descriptions of content.
consequentially, /g /s /fur /f /lit and to a lesser degree /rp /p2p /dis and even chat are about content-type, while /art /ai /3dcg and /kaki are about method of creation. only /req can be almost anything.
content types can mostly be added to each other (literature about furry guro including scat and so on), while methods of creation are mostly exclusive (either drawn, ai or 3dcg, though combinations are
rare but possible).
I am just adding that observation, because it complicates things when thinking about what goes where and what excludes what, especially when comparing scat/pee (content) to AI (art-style).