I had the same idea a while back and was wondering why no one has implemented something like this yet. This seems like an actual useful application for LLMs.
I am using Zotero (Citation Management Software) to collect scientific Articles I have read. Sometimes I forget in which Article I read about something specific. A search, where you could describe what you are looking for in a sentence, which then returns the Article with the relevant part, would be a gamechanger.
Thanks for the link! Learned something new today.