I think there is definitely space for niche search engines - there are tons of them already, if you include things like the DPLA, octopart, iconfinder.com, Spot

I think there is definitely space for niche search engines - there are tons of them already, if you include things like the DPLA, octopart, iconfinder.com, Spotify or class-central.com. Google is focused on getting you to a relevant result quickly, but having a search engine that helps you discover new things is really useful. If you focus on a niche, you can also make use of a lot of metadata Google doesn't retain. I'm exploring this on a small scale with https://www.findlectures.com https://www.findlectures.com. Having the date a video was made gives it a 'street view for history' feel, and lets me rank historical content differently from conferences (where recency is more important). Building a graph of talks, conferences / speakers / books / publishers could be the building blocks for a pagerank implementation, or to build a different type of book search. Alternately, I think it would be interesting if search engines let you do LSA style queries, like "Brian Goetz" - "Java" + "Python", to help discover speakers.