There was a question earlier in this thread (which I didn't save but meant
to respond to) about the impact of the addition of the GC. From what I
remember, the full dmd/druntime/phobos build and test cycle doubled in
duration. No one, that I recall, spent any time trying to diagnose or
improve it. Since we were up against a release, the choice was made to
pull it out until someone does have the time to actually work on it, not
just toss in an experiment.