Ah, I had forgotten that detail, Éric.

No, it doesn't seem as if implementing braces as matchers is appropriate.  fnmatch is only implementing the shell file name globbing. Doing the equivalent of brace expansion would have to be done before applying globbing, to be consistent with the shell.  Which is too bad.

Unfortunately I think we should probably reject this, though it could be discussed on python-ideas to see if the idea can lead to something both consistent with the shell and useful.