> There are other projects that have already added a fix for the new parameter positionally. If we add it to be the last (that still will break the old call) we would break them again.

Understandable


> The documentation never documented the arguments for the code type (probably on purpose)

Understandable as well, just thinking that a CYA sentence in types.rst: 
"These types are not supposed to be instantiated outside of CPython internals and constructor signatures can vary between python versions.

And maybe the docstrings. I rarely open the documentation on python.org and work most of the time by calling `help()` or `?` in IPython, so having some information saying this is non-public in the docstring would make sens to me. 

I'm happy to do it if it is deemed useful.