[Nix-dev] 6 month C4 adoption period

[stewart mackenzie]

rust is a fast moving target, I don't want too much breakage. Recently
upstream decided to shove experimental features into nightly releases
(ie the allocator we're using which broke our build), this would cause
huge breakage and annoyance ameliorating issues.

It's better to keep lockstep with Rust. Once those experimental
features *eventually* hit stable then I'll breathe a sigh of relief.
Till then, it's the march of wicked.