RE: Shouldn't custom.el load wid-edit.el?

["Drew Adams" <drew.adams@oracle.com>]

>     Shouldn't custom.el, which defines `defcustom', load wid-edit.el?
>
> No!  We don't want to load wid-edit.el all the time.
> We only load that when people start to make widgets.

But it means that `defcustom' does not recognize those built-in Emacs types
that wid-edit.el defines. Does it make sense that `defcustom' does not
recognize a predefined type such as `color' during the evaluation of its
:type sexp? For most Emacs users and Elisp programmers, :type is a
`defcustom' thing, not a widget thing - that's where they run into it.

`defcustom' predefined types are also widgets, and some of those are defined
in wid-edit.el.  custom.el doesn't stand on its own. Users, including
programmers, will expect `defcustom' types to be known by, well,
`defcustom'.

To repeat my question:

>> How else can [defcustom's] :type reasonably deal with types such
>> as `color' that are defined in wid-edit.el?