I noticed a patch sitting on #4412 tonight which seems interesting but
definitely needs a decision; the idea is that, rather than
implementing a separate widget or set of widgets to handle grouping of
options (via the HTML "optgroup" element), the Select and
SelectMultiple widgets should look at the structure of 'choices -- if
it has a nested structure of grouped choices, those should translate
into optgroups in the rendered widget.

Personally, I kind of like the simplicity of the approach and the fact
that it handles this use case without needlessly multiplying widgets,
so I'd give it a tentative +1.

--
"Bureaucrat Conrad, you are technically correct -- the best kind of correct."