I would still agree with his statement at least as far as BSD is concerned. Outside of Redox I haven't seen any serious projects to implement POSIX compatibility. The Rust coreutils project is a good start but from their readme it looks like they are more aiming to achieve GNU compatibility on Microsoft Windows while being MIT licensed — I don't think anyone is seriously using it to build a BSD (or even a GNU) distro. If I'm wrong about that I'd love to hear it though. Rust is a good choice to write these things in but let's be realistic about the time frame required to rewrite everything.
Plus I just downloaded those Rust coreutils and tried to build it and now I'm waiting for 400 (!!!) Rust dependencies to download and compile. Is this really appropriate for a core system component to have this many dependencies? Or is there something I'm missing here? I admit I am not familiar with best practices in Rust. As the project stabilizes I assume they will want to start eliminating the dependencies or vendoring them upstream? At what point do we decide to put these into a separate library like libbsd or gnulib?