This is awesome. I think it'd be useful to add filters for blocking sites that just copy SO and similar websites.
Agreed! I have lots of them in my list, using https://letsblock.it/filters/search-results as a template. I'm investigating adding presets to this filter (check a box to block the SO / github clones, they'll be added to the filter input alongside your blocked sites).
Reminds me of https://github.com/iorate/ublacklist
Hopefully you will add the startpage.com search engine (has same results as google) too :)