function elgg_register_widget_type() isn't apply this param.

Thanks Nikolai.  That's what I discovered.  Do you have any advice for setting and getting default widget options?

1. You can use widget_settings, <widget_handler> hook:

Triggered when saving a widget settings $params['params'] for widget $params['widget']. If handling saving the settings, the handler should return true to prevent the default code from running.

Look at this example.

2. Widget is an entity, so you can use it as the usual object via setting/getting metadata.

Of course, you need to know a GUID for this.

3. Don't forget, you can override the edit form of your widget by setting the default values before the user has done so.