Yes, it's plausible that were Rust to adopt Cranelift as a supported backend, you could use Cranelift as an intermediary to translate Rust MIR (via Cranelift CLIF) into C. Outputting functional-but-horrifying C would not be terribly difficult.
The CLIF format is low level but relatively architecture-independent.
The CLIF format is low level but relatively architecture-independent.