Debian, Rust, and librsvg

This is just wishful thinking. Rust is not C, that is, not all Rust can be 1:1 mapped to C. A lot of Rust is platform specific, so even if one could compile Rust to C, one would need a platform library abstracting syscalls, libc, compiler extensions, etc. wrapping the C systems APIs way beyond what libc offers.

Unless a big company pays 100 people to work on this full-time for a couple of years, this won't become production ready enough such that hobbyist can start modifying the parts required for the resulting C to even compile in the less supported platforms.

If you only want to target x86_64 linux with glibc, then this is doable, and some projects already try to do this. For anything else, there is a titanic amount of work required.

Just as an example, C has macros to support many platforms, Rust does so too. Imagine translating C with macros to Rust: you would have to first generate C without macros for each platform, then generate Rust code, and then recombine all that to generate
"portable Rust". The process from Rust to C isn't very different. Now think about all the nasty things that platform specific C code can use (pragmas, linking, ...).