Let's see, you can be extra safe and deny certain programs. Or be more "free", and break code when you introduce safer borrow checker.
It would literally break forward compatibility.
You know I really don't care for a pl that tells me how to do things. I fought python for a long time on a simple issue like indentation. C like syntax is best. RUST is stupid syntactically...surely you've noticed it's a leap. I'd use limbo before Rust.