>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.

I am +1 to such a sentence, but I think this is a decision that more core devs should agree on. Taking into account previous history (like the linked commit) and
the fact that promising stability on such internal pieces will prevent us from making critical optimizations I assume that others will agree, but I am still important
to know that there is a consensus.

I would recommend opening such PR if you have some time and let others review it as well.