The problem with the argparse backlog is that the original author of the module is too busy with other things.  And no one has stepped into his shoes.  There are people with experience in apply patches, and people who know the argparse code well, but few, if any with both skills (and/or the time to invest in this module).  

In addition the module has some serious backward compatibility issues.  I know of several patches that were applied, and then withdrawn because of unforseen (or at least untested) compatibility problems.  

While I commented earlier, I don't recall testing it.  I just tried it now, and ran into problems - until I realized this isn't compatible with Python2.7.  Py3 is the development world, but there's still a lot of PY2 use (e.g look at Stackoverflow argparse questions).  On SO if people have problems with FileType, I often recommend that they just accept the filename, and take care of opening it themselves.  

To raise the attention to this patch I'd suggest 

- making the case that it is really needed

- demonstrating that it has been field tested, and is free of backward compatibility issues.