I really appreciate the way Rust feature gates unstable features. It's easy to opt into nightly if you need them, it's nice that new features are iterated until they are correct and it is nice to rely on stable being stable.
"I'm sorry bryanlarsen, I'm afraid I can't do that." - 2023 a rustfmt Odyssey.
For the former then sure, it should just let you do the thing and simply fail loudly if it fails. For the latter, there's not much they can really do without switching you over to nightly rust.