The solution to the latest GotW problem is now available:

GotW #90 Solution: Factories (updated for C++11/14)

by Herb Sutter

From the article:

Guideline: A factory that produces a reference type should return a unique_ptr by default, or a shared_ptr if ownership is to be shared with the factory.

Guideline: A factory that produces a non-reference type should return a value by default, and throw an exception if it fails to create the object. If not creating the object can be a normal result, return an optional<> value.