Let me close this issue because its goal is too vague to be achieved. For instance if someone wants to add Nokogiri to core, please file a specific issue to request such thing.
I think nokogiri is not a good addition. Not because it is a bad
library, no, quite the opposite, but if I recall correctly it
depends on mini_portile2 (so this has to be included too, in
that case), and more importantly it requires compilation which
can fail (and failed for me in the past).