The paper on std::elide, P3288, has today gone from Revision 0 to Revision 1:

    http://www.virjacode.com/papers/p3288r1.htm

And here are the changes:

R0 => R1
    * The class std::elide is not defined as final
    * Template instantiation only fails if the constructor has exactly
one parameter.
    * Template instantiation fails based upon the presence of a
typedef tag whose value evaluates to true.