Joy2Key is a program for X and the console that monitors the joystick (typically /dev/js0) and sends X keyboard events to application windows or keystrokes to the console (both "terminal" and "rawconsole" modes for terminal stuff and SVGALIB stuff respectivly). It allows the use of a joystick with applications that don't otherwise support one, such as xkobo, iNES or sDoom. Joy2Key supports .rcfile and easy joystick calibration.
If I understand this correctly...
So what you're basically proposing is that command line programs provide a standardized way to print their command line options to stdout in a computer-readable format. Then GNOME can read in the command line parameter interface and use it to put up a slightly more helpful dialogue box for the user.
First, this requires modifying every application you might want to use through this system. That's a lot of programs, and good luck convincing people to do it. Second, command line interfaces tend to be more low-level than is useful for a GUI interface, so simply providing a list of the options doesn't actually make it any easier to use. Users who are comfortable with the command line can probably read the program's "-h" or "-?" output on their own just as easily. Users who don't understand how to use the command line probably won't understand the command line paramater description output, either. A more sophisticated wrapper around the program's functionality is usually called for in a GUI. Can this system provide that?