What would make this killer is if it automatically generated a top-notch bash completion script, like the kind that exists for git. There are very few that exploit the full potential. In fact, without that feature, this seems like overkill for a CLI. A CLI is already the simplest kind of interface, and it usually takes years for a tool to acquire that many features.
Although it seems like a great tool (and it is), when you start using docopt, it becomes tedious to check for complex command subcommand cases, for example, especially when you have lots of them, and you then switch to Click, JCommander, or the likes.
It would be a nice convention if CLI applications shipped a USAGE.txt or OPTIONS.txt file written in docopt in the root of their repo, along other standard files that one expects to be there like README.txt, requirements.txt, setup.py, project.json, etc.<p>That way it would be easier to write utilities for testing the CLI, to generate the shell completion script and to change the interface without messing with hard-coded strings in the code.
After using docopt for a while you're realize you don't want to google and trial&error text strings somewhere in the file and eventually switch to argtools to realize how easy it can really be ;)
Hm! I once looked at auto-generating GUI wrappers for command line programs from their manpage syntax, but it turned out that manpage syntax, while it <i>looks</i> standardised to a human, isn't. This would open a lot of really exciting possibilities if it were more widely used.