Huh, isn't struct B literally what an implementation of std::box would look like? You would need a nullptr check in the copy ctor and copy assignment operator to make it complete, but other than that, that is exactly how I would implement box. Anything that would be in std, you can implement yourself, so I would encourage people to try implementing box themselves and see how it works for them.
Yes, it's not too difficult (but thanks for the pointer, edited). The question was why this smart pointer would be useful at all, not just whether it belongs in the standard library. Implementing the helper class yourself is not too bad, but putting this in domain classes is a lot of cruft.
