This is the key question. In an ideal world it would parse Doxygen-compatible comments and output to the Doxygen XML file format so it can then be rendered by D

This is the key question. In an ideal world it would parse Doxygen-compatible comments and output to the Doxygen XML file format so it can then be rendered by Doxygen's HTML generator. Keep this tool focussed on the parsing etc. and let Doxygen continue to do what it does well. In my mind Doxygen is a fantastic tool and its only drawback in my experience is its slightly simplistic parsing engine which means it's slow to adapt to new language features.