This proposal aims to provide guaranteed copy elision for common cases of local variables being returned from a function.
The accepted P0135 proposal already provides guaranteed copy elision for when a prvalue is returned from a function by stating that the result object of that prvalue (and not a temporary) is directly copy-initialized. It de-facto mandates what was known as Return Value Optimization (RVO) and allows non-movable objects to be returned in such a way.
Meanwhile, other cases of copy elision are still optional. For example, sometimes we want to create an object, set it up and return it.