What really makes me say that is that a lot of things we have recently asked for gcc-specific extensions are in fact relatively easy to implement in standard C++ and, in many cases, allows for infrastructure improvement *without* global code changes (see below.)
C++14 is in my option the "minimum" version that has reasonable metaprogramming support has most of it without the type hell of earlier versions (C++11 had most of it, but C++14 fills in some key missing pieces).