Honestly, I think the more reliable curated information will be what I miss the most. I almost always append a Google search with "Reddit" - because the information and format are so much more reliable than the bot populated garbage sites.
Already today I've made probably 15 Google searches with the "reddit" suffix only to be met with privated subreddits. It's a grim feeling, considering my undying support for sticking it to Reddit rn. It kind of feels like passing by the place old restaurant that was always nasty and unhygenic yet had delicious nostalgic food, and remembering that the place eventually closed down and you won't get that experience anymore.
RE niche porn subs, same here brother 🙌 Seems pretty slim atm on Lemmy but I am sure it will grow. Have seen a couple. Trying to do my part as well and manage one if you are interested in 'the posterior':
I think ChatGPT is going to mean Reddit and similar sites will also become bot populated garbage. There was just now a major problem with this in /r/programming.
Probably, if it gets big enough to attract that kind of attention.
What concerns me the most isn't the spam for karma that we have seen on /r/programming, but commercial spam with genuine-looking comments about a product. I used to use Reddit to review products before buying them because Amazon reviews etc. are so infested with bots and fake reviews. But now it seems forums will be no better.