Someone will have the fun of writing those wrappers, because Google won't do it.

Likewise a future Fuchsia Studio won't support templates, debugging, or OS libraries written in Rust.

And the Fuchsia team most likely won't prioritize toolchain bugs related to Rust.

This is the biggest difference between using an official SDK language and guest languages.

Rust doesn't have a stable ABI, so it's sensible to always go through C bindings anyway. The other things you mention are just a matter of what their future Fuchsia Studio chooses to support.