Many new features are landing in C++20, which will make the library easier to extend with new features: concepts, operator<=>, constexpr algorithms, parts of the Ranges TS if not the whole Ranges TS itself...

All these features will directly the library in that it will help to implement several features that are currently hard to implement with C++14 only and where C++17 doesn't help much. While the idea of the library would remain the same, C++14 compatibility would be lost and maintaining a hybrid version with conditionally-enabled C++20 features looks like too much work, so a breaking change is needed to provide the new features: cpp-sort 2.0.0 as a C++20 library seems to be the solution.

Several questions remain:

• Can we conditionally enable parallel algorithms in the 1.X branch when they are available or should we only provide them in the C++20 branch?
• If the Ranges TS isn't incorporated in C++20, do we wait for another release?