With the XML craze in full frenzy, SGML is being pushed into the background even more, for all but diehards. This is a pity, because SGML has a number of very useful features that didn't make the cut for the first (and to date only) version of XML.
Even so, SGML isn't without faults. There's room for improvement.
Taking Annex K.4.4 of the WebSGML TC to its limit.
Getting rid of a nasty difficulty in ISO 8879
Addressing context by other attributes.
Not much, IMHO!
A way to combine XML Namespaces and SGML Architectural Forms
A broadside on XML namespaces, which I have always considered worse than useless.
A Usenet post explaining the basics of mapping names, and how XML Namespaces got this hopelessly wrong.
The first part of a write-up (in May 2003) of the issues with XML namespaces. Some of these were brought out in a long thread on the xml-dev list.