Context: I was trying to search the linux kernel bugzilla and mailing list to find specific mentions to my laptop model, turns out the content there is very badly indexed given the importance of such discussion place, even when filtering to a specific website or a specific term using quotes or "site:X" (not a Kagi specific problem, all of the popular search engines failed)
IIRC Teclis allowed to submit specific websites so it can crawl. I never really tested so I don't know if such search would be better overall.
Idea: Allow the users (maybe only paying ones to limit spam) to submit specific websites for a thorough crawling that will have a higher quality (I'm talking algolia like quality).