I hope it's not too impudent to request a new ebuild, similar to bug 15347, for Docbook SGML 4.3. Since they are already working on a 4.4 beta, I believe that it has been out for quite a while. This new version offers quite a few new things, and the O'Reilly Docbook Guide refers to many of these... failure of these new features to work on my computer is how I realized that Gentoo still offers only an older version of Docbook SGML.
Added to CVS. Thanks for reporting.