Proposed resolution (September, 2015):

Change 6.8 [basic.types] bullet 10.5 as follows:

A type is a literal type if it is:

• ...

• a possibly cv-qualified class type (Clause 11 [class]) that has all of the following properties:

• it has a trivial destructor,

• it is an aggregate type (9.4.2 [dcl.init.aggr]) or has at least one constexpr constructor or constructor template that is not a copy or move constructor, and

• if it is a union, at least one of its non-static data members is of non-volatile literal type, and

• if it is not a union, all of its non-static data members and base classes are of non-volatile literal types.

[Adopted at the February, 2016 meeting.]

According to 6.8 [basic.types] bullet 10.5.3, all the members of a class type must be of non-volatile literal types. This seems overly constraining for unions; it would seem to be sufficient if at least one of its non-static members were of a literal type.