[Adopted at the February, 2016 meeting.]

According to 13.2 [temp.param] paragraph11,

If a template-parameter of a class template or alias template has a default template-argument, each subsequent template-parameter shall either have a default template-argument supplied or be a template parameter pack. If a template-parameter of a primary class template or alias template is a template parameter pack, it shall be the last template-parameter.

These requirements should apply to variable templates as well.