Why is the size not a template argument of std::initializer_list?

Question

std::initializer_list is constructed by the compiler from a brace-enclosed init list and the size of this list must be a compile time constant.

So why did the committee decide to omit the size from the template arguments? This possibly prevents some optimizations and makes some things impossible (initializing std::array from a std::initializer_list).

Answer 1

One upside of the existing system is that you can export functions which take an initializer_list from a DLL. If it were templated on the size, they would have to be shipped as source.