If you haven't heard of Brave Goggles (https://github.com/brave/goggles-quickstart) I highly recommend checking it out. Just being able to create the search index is a massive task, so being able to apply rules server-side to their "expanded recall set" will give you what most people building search engines want, which is to control the algorithm. We weren't able to do that until now since applying rules client-side doesn't work well on a small search result set.

Related: I created a tool to create Goggles using subreddits as a signal source for domains: https://github.com/forcesunseen/narwhalizer