Since you have domain expertise, I'd love to know your opinion on searching through "personal libraries" like Zettelkasten (or similar repositories), and perhaps linking that with Internet-scale indexes.
Are there tools that do that well right now? Do you know of (maybe niche) projects exploring such ideas?
There are a lot of pitfalls and erroneous assumptions built into both Google's current search and the information used to train AI/ML models. Two big ones are "assuming that a person searching for something and accepting the answer means it's a successful search" and "assuming a person searching/asking for something actually wants what they're asking for".
I'm a librarian with several years of reference experience under my belt and neither of those things are true. They're both good tools for a well considered and well informed information search, but that 'well considered and well informed' is doing a lot of heavy lifting.