I hooked up support for XInclude in librsvg today (without support for the XPointer attribute). I've also been talking with Peter Moulder from Inkscape team. It seems that they forked the libcroco CSS2 engine a while ago in order to improve its selection engine. Libcroco's selector is sub-optimal now, in that it needs to operate on a libxml2 DOM tree rather than the DOM-like trees that Inkscape and Librsvg use internally. Inkscape's version corrects this, and we're working on getting the trees merged, thus eliminating the fork. Hopefully we'll get this straightened out soon, so that librsvg 2.16 will have really good CSS2 support.