Dynamic custom fieldsets for Webform Integration

The basic workflow would be that:

• User 1 would create a form for collecting case and activity data.
• User 1 can configure the form so that a "set" of custom fields would be displayed.
• There would then be another user (user 2) (who does not have access to the webform to make changes) but would have CiviCRM admin access. User 2 should then be able to modify the custom fields in the set defined above say to add another field.
  This new field should then be dynamically shown on the webform without User 1 needing to make any new configuration changes.

I've put together a quick sketch of how the admin UI for webform could be implemented. This is shown for Activities only but we would want support for Activities and Case custom field sets. I'd welcome your feedback on this approach and specifically the display options on the webform side.

As a note its quite important to us that from a technical perspective that the webform configuration itself does not get updated when the custom fields are changed, but that there is a single "token" in the webform that represents the field set that is then generated dynamically when the form is rendered. Let me know if you have any questions on this point.