Roadmap for 2.0

overhaul serialize/pretty printing API

https://github.com/tenderlove/nokogiri/issues/530 XHTML formatting can't be turned off
https://github.com/tenderlove/nokogiri/issues/415 XML formatting should be no formatting

overhaul and optimize the SAX parsing

see fairy wing throwdown - SAX parsing is wicked slow.

improve CSS query parsing

https://github.com/tenderlove/nokogiri/issues/528 support :not() with a nontrivial argument, like :not(div p.c)
https://github.com/tenderlove/nokogiri/issues/451 chained :not pseudoselectors
better jQuery selector support:
https://github.com/tenderlove/nokogiri/issues/394 nth-of-type is wrong, and possibly other selectors as well
https://github.com/tenderlove/nokogiri/issues/309 incorrect query being executed
https://github.com/tenderlove/nokogiri/issues/350 :has is wrong?

DocumentFragment

there are a few tickets about searches not working properly if you use or do not use the context node as part of the search.

Better Syntax for custom XPath function handler

https://github.com/tenderlove/nokogiri/pull/464

Encoding

We have a lot of issues open around encoding. Is this really an issue? Somebody who knows something about encoding, and cares, should point this one.

Reader

It's fundamentally broken, in that we can't stop people from crashing their application if they want to use object reference unsafely.