DDMD and such.

[Gor Gyolchanyan]

I know, this has been discussed earlier, but i don't quite understand
the real reason why isn't DMD's front-end being written in D.
Existing DDMD is pointless (and i think abandoned), because it's just
a plain rewrite with the same C-style constructs and completely
rewriting it to be a correct D code would mean being unable to get the
bug-fixes on DMD.
I remember, that Walter said about the problems with compatibility
with the back-end, that would arise.
But isn't D supposed to be binary compatible with C?
AFAIK the only extra thing to be done would be to provide a C facade
around the D front-end, that would be given to the back-end.
Why not?