alt Hacker NewsSafe threading seems like fully exploiting hardware features to me. That's the biggest thing smart pointers and Rc, Arc, and Cell types enable. Perhaps I could have been clearer.
The comment about memory layout was an additional point that dealing with hardware requires that you format, align, and position information in memory as the hardware expects, which requires either exposing those details, or encoding them in a runtime.
Safe threading sounds great, as long as the language gets out of my way when I absolutely do not care about safe threading.
I write compilers (and have contributed to the Rust compiler!), and there has been approximately zero times in twenty or so years that thread safety has been a concern.