Dimitry SibiryakovAnatoly MoskovskyЭту тоже не разрешает.

Однако, разрешает:
cppreference3) if T is an array type, each element of the array is
value-initialized;

A a[10](5); это не value initialization, а direct initialization.
http://eel.is/c draft/dcl.init#17 The semantics of initializers are as follows.
The destination type is the type of the object or reference being initialized and the source type is the type of the initializer expression.
If the initializer is not a single (possibly parenthesized) expression, the source type is not defined.

— If the initializer is a (non-parenthesized) braced-init-list or is = braced-init-list, the object or reference is list-initialized.
— If the destination type is a reference type, see [dcl.init.ref].
— If the destination type is an array of characters, an array of char16_­t, an array of char32_­t, or an array of wchar_­t, and the initializer is a string literal, see [dcl.init.string].
— If the initializer is (), the object is value-initialized.
— Otherwise, if the destination type is an array, the program is ill-formed.Anatoly Moskovsky, конечно, будет говорить, что "Otherwise" относится только к предыдущему пункту ("If the initializer is (), the object is value-initialized."), но не надо его слушать.
"Otherwise" относится ко всем вышеперечисленным. Инициализатор в `A a[10](5)` не попадает ни под одно условие выше пункта с Otherwise, а destination type is an array. Следовательно, the program is ill-formed.