No, this is overly simplistic. The features in the quoted comment are largely things that nobody other than stdlib developers need to understand. There is no bespoke subset-dialect of Rust where people are tossing around the `fundamental` attribute--it is strictly an obscure detail that not even an expert Rust programmer would be expected to have even heard of.
The main issue with "fundamental" is that it's currently unstable, but a stable version of it could definitely be useful for lessening the "orphan rule" constraints on implementing traits. Probably would want a different name such as #[deorphan] though.
