The Rust language team wants a more general solution that also works with types like `Arc`, instead of hardcoding a special case for `Box` into the language. This is generally called "deref patterns." But there are tricky open design questions, so the effort is stalled until someone comes up with a proposal addressing them

I believe it's not stable because it gives std::boxed::Box special treatment in the language. They'd rather find a solution that could work equally well for smart pointers defined outside of std.

Box patterns are likely to be superseded by one of these:

https://github.com/rust-lang/rust/issues/42640

https://github.com/rust-lang/rust/issues/87121