This bloats the std library and forces lots more work and stress on the rust dev team. Not to mention it’ll add more churn to the std lib.
My argument would be that if a more featureful standard library could get Rust closer to the superior dependency culture of Go, it'd be worth it. As-is, Rust dependency trees are just wild.
Also, I think that your example of Go's breaking crypto changes misses the forest for the trees--the stdlib has been incredibly stable through its history, and the vast majority of packages just never have to worry about it. I'm honestly not aware of a language out there with similar adoption, featureset, and robustness. More to the point, I'm not aware of a language out there with a more reliable stdlib that permits the ecosystem to have small dependency graphs.