The discussion about merging the GNU D Compiler (GDC) into the GNU Compiler Collection was brought up again today on the GCC mailing list. Right now they've got the license to the D front-end transferred over to the Free Software Foundation. The copyright assignment is needed by the FSF for this code to be merged into the GCC code-base.
Among the active concerns is having maintainer(s) for the GCC side of the GDC front-end, so that this support will not become stale or go un-maintained once merged. There's also some other technical concerns expressed in the aforementioned mailing list thread, for those interested in learning more. At least it looks like the ball is finally rolling again to get the D support merged into GCC.
For those wanting to learn more about the D programming language, visit Wikipedia or Digital Mars (the company largely behind the D computer programming language).