I am not sure if I remember everything correctly, but from a discussion on the developer mailinglist I think X stuff (XPath, XQuery maybe XForms) are being implemented in a subproject calle KDOM2, also used or to be used by the SVG module KSVG.
I can't remember if there has been a final decision if KHTML will depend on it or take the parts it needs and build the rendering structure around that.
You might find the thread in the archives, it was either on kfm-devel (the Konqueror development list) or on kde-core-devel
Cheers,
_