There is now a proposal to switch Rustc Nightly to use a parallel frontend

The work has been going on for some time now and it seems we are quite close to it being enabled as a default for nightly builds, I am super thrilled upwards of 20% faster clean builds and possibly more are on the horizon. Hope everything works out without triggering some unseen ICE.
https://github.com/rust-lang/compiler-team/issues/681