C++ compiler vs D compiler

[Abdulhaq via Digitalmars-d]

Perhaps the answer to this is obvious, but what's harder to write 
from scratch - a C++ compiler or a D compiler? :-)

We know Walter wrote a C++ compiler single handedly, does anyone 
else recall the C++ Grandmaster qualification, the free course 
where participants get to write a complete C++ compiler from 
scratch? I think it's dead now but I can't find any real info 
about that despite a serious google. What's the chances of anyone 
single-handedly writing a D compiler from scratch in the future? 
I know deadalnix is writing SDC in D - sounds interesting. Is the 
D language well enough documented / specified for a complete D 
implementation to be even possible (as things stand now)?