I am wondering whether this would actually be a helpful compile option in upstream rustc for quick prototyping. I don't want prod code to use this, but if I want to try things out during development, this could substantially shorten the dev cycle.
What the point, though? You will get compiling code, but later you would need to reachitecture code to avoid violating rust rules.
After a while, you just don't write code that would cause substantial borrow-checker problems, even when prototyping. I'd say the slow compile times are much more of an impediment for a practicing Rust prototyper than the borrow checker.