The std::optional in MSVC was implemented in a language considerably behind current C++, for obvious reasons. The need to use template metaprogramming in implementations is much less, today.
How so? Some of the "enable_if"s can probably be replaced with "requires" syntax, as well as the "conjunction_v"s and "disjunction_v"s, but the majority of the complexity seems to be in expressing the various requirements imposed by the Standard. Are there recently-added concepts (or other features) that would express them more naturally?