This could be used within https://bootstrappable.org/projects.html to make bootstrappability of rust incredibly much easier other than the previous route of OCaml and other things.
I know some folks within the bootstrappable OS projects community are on Hackernews and I hope that they could take a look at this. I feel as if this project could drastically shrink down the efforts needed to get a working rust compiler in a bootstrappable manner.
mrustc (a handwritten Rust compiler in C++) is already used for that in Guix and likely other distros: https://guix.gnu.org/blog/2018/bootstrapping-rust/ This would have other benefits though, as it's both a second bootstrapping path and could potentially compile Rust programs for platforms not supported by LLVM
Not really. This C code is more like a binary and compiler artifact than a source code. So it won't match the standards of bootstrap.
Depending on what your goal is. If it is eliminating trusting trust attacks, yes this is no enough. But more commonly you only want to compile rustc for a platform it was never compiled on, and for that this project is definitely enough.