I've wondered recently if this simple (but powerful) feature would be enough of a differentiator for a search engine challenger to gain serious market share.

Imagine if Duck Duck Go offered that by default?

There are several such differentiators:

- exclude walled gardens

- exclude sites with ads and/or ecommerce

- exclude sites with tracking

- exclude sites with fixed headers

- allow users to have personal blocklists

As a bonus, if you make a new search engine offering such options, existing search engines will be afraid to copy them.