An even more modest proposal...

[Ben Cooley]

Allow D to import a GCC-XML or an alternative xml file with the class hierarchy,
structure layout, members, methods, and macros defined in a c or cpp header, and
be able to access members, call non-inlined methods, or auto-generate a .cpp
file with cpp code or functions for inline methods calls or template
instantiations in D.

This would eliminate the need for D to be responsible for parsing Cpp, and
directly provide the D with the information it needed to interoperate with
existing C or Cpp libraries and code.  The responsibility of generating that
file would be from an externally supported Cpp parser like GCC XML, Elsa, or
Swig.

D = Cpp/CLI ....  XML = CLI.  That would be an apples to apples comparison.

How you generate that XML file is your problem.