Recommend that this be closed with no action taken.  It is an important
step for Py3.x that old style classes be left behind and that no mention
of them occur in the 3.x docs.  Let's not carry 2.x with us into the 3.x
world.  The whole point was to leave the old world behind.

Also, the issue is not new in the sense that any cross-version pickling
may exercise functions or classes that did not exist in other versions
or whose meaning changed over time.  This is the nature of cross-version
pickling.

If someone wants to make pickling notes on the Python wiki, that would
be fine.  The pickling docs are already somewhat lengthy and complex,
yet will never cover every issue someone could think up.