XML has really proven to be a more than adequate replacement for SGML
XML can do everything SGML can do. It's not just for the smaller, simpler projects as originally planned.
Very few if any new SGML projects, either documents or software, have been launched in the last couple of years. All the new effort is going into XML.
Many old SGML projects (DocBook, TEI, CML, etc.) are transitioning to XML
Reality exceeded the hype