If you're mixing target configuration via GNU config.sub (for example, GCC, including GCC/Rust, or generally GNU Autotools) with non-GNU config.sub (for example, Rust), then yes, you'll need some kind of (bidirectional) mapping table for target plus any relevant other flags that may be implicit in the target string.
@zackw, would it make sense to host this translation table in config.sub, with a new mode/command-line flag? (If that makes sense?)
@InfernoDeity, I'm not sure I got what exactly your actual concern or suggestion is?