I agree with most of that, but there's one important detail (that I'm sure the designers of this proposal are thinking about): The current contract of Pin in Rust (the only standard support for expressing immobility) doesn't just cover the object's own location, but also any references derived from the object, commonly called "pin projection".

For example, if you have a `Pin<Box<Vec<u8>>>`, it's safe to turn that into a `Pin<&mut [u8]>`.

Any system that replaces `Pin` will probably have to maintain that same property, which wouldn't naïvely happen using C++-like move semantics, right? Or maybe I'm overassuming?