I think the primary reason Rust doesn't do this is because it's a semver hazard. I.e., adding a non-Copy field would silently break downstream dependents. Yeah,

I think the primary reason Rust doesn't do this is because it's a semver hazard. I.e., adding a non-Copy field would silently break downstream dependents. Yeah, this is already a problem with the existing auto traits, but types that don't implement those are rarer than types that don't implement Copy.