So, I tried making some guro images using the new NAI4. I'm glad to report that it is generally better than NAI3.
Firstly, they got the intestines right. NAI3 didn't understand that intestine and organs are supposed to come out from the person's body, and just spread the organs all over the place like Saya No Uta, often making furniture or other objects with organs, forcing me to use a dozen tags on negative prompt to get a better chance, which still requires dozens of gacha to get one right.
When NAI4 draws intestines, it properly gut up the target person, or at least place it very close to its torso, so not only I get to remove some of the negative tags, the overall odds of getting a decent guro image has greatly increased.