Rust is suitable for a great deal of what C is used for (extending higher-level languages, writing language-agnostic libraries, embedded development, etc.) but Rust will likely never support as wide a variety of obscure platforms as C does. That said, Rust already supports Linux, OS X, Windows, and Android as first-class citizens, and support for FreeBSD, iOS, PSP, and lots of embedded and ARM platforms is currently provided by the community.