The big dates for SGML are 1986, when the IS 8879 standard finally was published; 1990, when editor Charles Goldfarb’s annotated version The SGML Handbook came out, and 1996 when XML was mooted at the SGML ‘96 conference. Charles once told me that when IS 8879 first came out, they half expected it to take over the world; only to be utterly mystifyingly held back by WYSIWYG, which stole the usability thunder from SGML. Well, after 20 years, “WYSIWYG is dead” and markup is king. Or, at least, WYSIWYG now uses styles and flexible window sizing, and SGML has succeeded by abandoning the Wiki-like markup feataures.
The minor dates for SGML were 1988 (insignificant change), the ENR corrigenda in 1996 on extended naming rules (which I drafted), the WebSGML corrigenda in 1999 to encourage and endorse XML, and XML 1.1 (which may yet come into its own at some time, when XML 1.1 parsers are ubiquitous.) As SGML became refomulated as XML, DSSSL was reformulated as XSL-FO, SDQL was completely reworked as XPath, DSSSL transformations became XSLT, HyTime was joined trapped in the starting stalls by Xlink, GROVES vagued out into XML Infoset, architectural forms & DTDs influenced XML Schemas, SDIF looks like having an analog in the binary infoset (”Efficient XML”) work, and the various calls for modularity found a more amenable home than the SGML revision process as XML Namespaces.
The ancillary material around SGML is still be maintained at ISO. In the last few years, for example, the ISO stnadard public entity sets have been enhanced for better maths support, with input from W3C Maths people, STIX and the Unicode Consortium. These entity sets may have a new lease on life if, as it currently looks, the Document Schema Renaming Language (DSRL) provides the mappings to allow entities in XML without ENTITY declarations.
Looking through that conference proceedings today, there are many usual suspects still active: Jonathan Robie on XML databases went on to XQuery, Bob DuCharme talked on free software, Jon Bosak talked about the need for a mini-DSSSL for online work, Tony Graham talked on internationalization, Lauren Wood, Timn Bray, Tommy Usdin and many others.