C-Extension support is still not complete and comes at a massive overhead. That's better than no support at all but the performance impact might be a problem in

C-Extension support is still not complete and comes at a massive overhead. That's better than no support at all but the performance impact might be a problem in some cases. PyPy is also still several versions behind implementing the latest Python 3. So while PyPy is definitely a great project, groundbreaking in many ways and a very useful for a lot of applications, it's not a replacement for all applications, for now at least. Also while the actual PyPy Python interpreter is reasonably simple overall the project is incredibly complex. It at least appears as if there are parts of the PyPy project not even all PyPy developers understand. Making PyPy the reference implementation is probably questionable for that reason alone.