If WG21 were handling Rust instead f64 would implement Ord, and people would just write unsafe blocks with no explanation in the implementation of supposedly "safe" functions. Rust's technology doesn't care but their culture does.

Beyond that though, the profiles idea is dead in the water because it doesn't deliver composition. Rust's safety composes. Jim's safe Activity crate, Sarah's safe Animals crate and Dave's safe Networking crate compose to let me work with a safe IPv6-capable juggling donkey even though Jim, Sarah and Save have never met and had no idea I would try that.

A hypothetical C++ 29 type safe Activity module, combined with a thread safe Animals module, and a resource leak safe Networking module doesn't even get you something that will definitely work, let alone deliver any particular safety.