This project sounds kind of masochistic but the idea is to bootstrap Rust from tinycc, and have traceability down to the lowest level assembly code. There is a step missing though? Tinycc is written in C after all.
I think it would make more sense to bootstrap from a small Lisp written in assembly language, if the traceability goal is worthwhile at all. There is nothing special about C.
The main thing is that TinyCC has already been bootstrapped.
Check out this page on bootstrappable.org. Basically they start with a 200 something byte binary (hex0) that can act as an assembler, then using a bunch of layers of tools and compilers you can bootstrap a whole system. I think they use stage0 to build M2-Planet, use that to build GNU Mes, and use that to build TinyCC.
So a project like this fits neatly into that bootstrapping path. It could be done other ways, but starting from a fairly complete C compiler makes it a lot easier than building an entire path from scratch.