Create both public and private Sections within the same Space

I have entered this feature request to be able to satisfy the following use case:

Use case (as described in support request [1]:
A company is structured into departments. Each department has their own Space. Department employees are Space members. Department management is responsible for managing membership of the Space.
A department will publish information in this Space that is public to the company. Each department will also publish information that is to be read only within the department. The department management will have their own set of pages that only they can read.

This results in the following setup:
One Space per department
(1) A public section within this space
(2) A section accessible to the whole department but not to the rest of the organization
(3) A private section accessible to only department management

This can be currently realized as follows:
(1) - create a public Section in the Space, no access restrictions
(3) - create a private Section in the Space, add department management as a Team to the access restrictions of this section

However, there is no easy way to realize (2), restrict a Section to all the members in a Space.

Schematic: [2]

Workarounds:
There are some workarounds, which I described in [1]. Furthermore, John gave me another workaround in the same article. However, these workarounds all introduce an extra level of complexity (either a subspace, or a Group that overlaps with the Space, or a Team that overlaps with the Space), which complicates administration for department management. This is unnecessary, because the target audience is already known (Space members), and security therefore can be enforced through the 'Group Content Visibility' field.

Proposed solution and feature:
I propose

• to add the 'Group Content Visibility' field as a default to the Section Page content type
• can be modified to select Public or Private

• to add the 'Group Content Visibility' field as a default to all content types that are Section Nodes (like Discussion Post and Event)
• default value inherited from the parent Section
• fixed value, inherited from parent Section, so that if parent Section is changed from Private to Public, the Section Nodes follow.

If there is any more information I should provide, please let me know.

Thank you,
Mark.

====================================================================================

Further information:
The mechanism of inheritance was mentioned in [3] for oa_section_ref.
The proposed solution should also work for custom Section types as described in [4]
A similar use case (without solution) was described in another issue [5]

References:
[1] Original question:
Structuring public and private sections within a space
https://www.drupal.org/node/2303885

[2] Attachment:
Functional diagram
https://www.drupal.org/files/issues/PrivateSpacesv001.png

[3] Mechanism of inheritance (oa_section_ref, reference to oa_section_context.module):
'Add section content' block does not pass source section to node form
https://www.drupal.org/node/2174981

[4] Custom content types:
Custom Content Type for Section Page
https://www.drupal.org/node/2194565

[5] Possibly related:
Best practice on sharing private content with the general public
https://www.drupal.org/node/2313351