This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
The definition of a “potentially-overlapping subobject” in 6.7.2 [intro.object] paragraph 7 does not exclude non-class subobjects; in particular, 9.12.11 [dcl.attr.nouniqueaddr] makes no restrictions on the types of members declared with the no_unique_address attribute. It is not clear that a potentially-overlapping scalar member or array of scalar elements is useful. Should there be a restriction on the type of potentially-overlapping subjects?
Restricting the type of a potentially-overlapping subobject would make it difficult to use no_unique_address on a subobject of dependent type, which may be a non-class type in some, but not all, specializations. Compilers can warn about non-sensical uses in non-dependent contexts.