Is it feasible to slowly rewrite a C++ codebase in D?

[Jordi Gutiérrez Hermoso]

I'm specifically thinking of the GNU Octave codebase:

http://hg.savannah.gnu.org/hgweb/octave/file/@

It's a fairly old and complicated C++ codebase. I would like to 
see if I could slowly introduce some D in it, anywhere.

Now, as I understand it, I would need to begin with making `main` 
a D function, because D needs to initialise the runtime. Is this 
correct?

Another possibility might be in dlopen'able functions. Currently 
Octave uses so-called oct functions, which are nothing more than 
C++ object code that is dynamically loaded by the interpreter at 
runtime. They are compiled to the Octave C++ API, but we also 
have a Matlab-compatible C API that perhaps could be more 
amenable for D-ification.

What are your ideas?