Docs look good as mentioned there, for the current behavior, although it would be good to improve the behavior.  

Note that I have supplied a wrapper (t18a.py) (if it hasn't bit-rotted for 3.4, I'm still using 3.3) that provides the needed functionality. The problem is, that I have no clue how to modify the internals of argparse to allow it to simply be a method of the current argparse class.  One could achieve the goal by renaming the current argparse class to _argparse, and renaming my wrapper class to be the "real" argparse, and that would work, but would seem to be inefficient.

It would be nice if someone could move the needed functionality, a new API called parse_intermixed_args, already approved by msg166175, that does the same thing as my wrapper does, but without the wrapper class. This would be a cure to the problem, and it could be tested against my wrapper class by comparison to ensure the needed functionality is provided. I'd be glad to help with testing and understanding the requirements, but don't have time to figure out the internals of argparse at present.