I make very little use of Kagi's value-add features. Like, I think I use a bang or two, but I can replicate that in the browser with Firefox bookmark keywords and a bit of configuration. They have dark mode, but I can do that (at the cost of a bit of slowdown) on websites with Dark Reader. I do use the "search the Threadiverse" feature, which they call "Fediverse Forums". But outside of that, I really just care about the no-log no-profile privacy stuff, which is what really interests me. Well, and not having to fight with a search engine over putting ads in is handy, but thus far, ad-blockers have managed to stay ahead.
However, I did think of one feature that would be kind of neat, though I don't know how much value it'd have to most today.
With a lot of work and digging up comments and such, people managed to reconstruct most of what was searchable at one point. There was a point where I think AltaVista was running a Usenet index. Then Google acquired them and linked it into their Google Groups search, which last I looked was kinda broken and mingled data from other forums that Google had indexed.
I don't know if anyone else (The Internet Archive?) has indexed that. Might be interesting for them to index that; current search engines won't do that.
kagis
It looks like at least as of three years ago, Google Groups still could provide Usenet data and still was kinda broken:
https://old.reddit.com/r/usenet/comments/zn8x6a/searching_for_old_usenet_posts/
It looks like someone's running an archive at usenetarchives.com with limited searchability (I.e. just a string from the text).
He announced it on Reddit here, and it sounds like it's a volunteer thing supported by donations, so I dunno if it'll be up forever.
https://old.reddit.com/r/usenet/comments/in6u06/free_usenet_text_archive_goes_online_300_million/
Ah, and it wasn't AltaVista, based on this post. Was DejaNews.