I original thought @tophee was referring to the Site Settings too, but it turns out it already supports searching with spaces:
https://github.com/discourse/discourse/commit/a78458300481a4e4505b829a30ef73d52fdf9b04
then I re-read the OP:
When I searched for
"enable local logins via email"(a site setting) an hour ago, I was surprised not to find a single post.
which led me to believe it is actually referring to /search page.