At a quick glance, I think you've got the right idea.  Fixing this involves a lot of PyArg_ParseTuple -> PyArg_ParseTupleAndKeywords upgrades all over the place.

Obviously there are are a wide range of things that can use updating for this so in order to keep things sane, it makes sense to do them in stages with individual patches for particular libraries.

I like that your 8706_2.patch chose to attack stringlib to start with as that covers a lot of ground with one piece of code and that you updated the tests to confirm that ordered args and keyword args both work.

This issue as filed doesn't have a well defined "end goal" to know when it is complete.  Another good thing would be to come up with a final goal.  Perhaps an audit of the stdlib and types to list which things do not properly accept keyword arguments?  That way there is a list of things to check off.  And if desired we could file sub-issues for various components rather than letting this one get huge.