Rationale (November, 2010):

The CWG did not see a correlation between the explicitness of a base class constructor and that of an implicitly-declared derived class constructor.

Paper N2987 suggests that an implicitly-declared copy or move constructor should be explicit if the corresponding constructor of any of its subobjects is explicit. During the discussion at the October, 2009 meeting, the CWG deemed this a separable question from the major emphasis of that paper, and this issue was opened as a placeholder for that discussion.

See also issue 1051.