[cmrdporcupine]

The amount of things that have to happen for a modification to the build environment for a target is more than just that the tooling exists and is supported on those platforms.

Picking just one piece: Consider that Chromium builds happen in a distributed build farm. There's multiple variants of this (goma, rbe). I'd imagine those systems would have to be modified to support the Rust toolchain for that target.

And it looks like this work is built around making GN/ninja support Rust, just using cargo directly. So that's what they likely mean by "not as rich as other languages yet."