As much as I like the CLI, I really find this useful, because it takes time to go through document and find the desired option. I think the real solution is that every CLI program comes with a description file (probably in XML) that describes its CLI options, their types, combination, etc. The description file should help automatic GUI creating or shell completion.
I think you just described a man page. Except for the xml part. That sounds a lot more like something MS would do.
I agree that this might lead to something which is not in Unix spirit but already shell completion provide such information and this shows the need for such specs.