Problem/Motivation
Now we have Drupal 8 and positively encourage developers to create multiple types of content entity, we need to stop assuming that all content is made from nodes. Even in core drupal, we have node content, comments, files, custom blocks, taxonomy terms and more. As of 8.4 we also have Media.
Proposed resolution
Change the menu admin/content to use the same page layout as admin/structure and then have the current node content view a sub page of that, the comments views another sub page, etc etc.
Remaining tasks
User interface changes
The admin/content routes (and below) will change to more reflect that in admin/structure
API changes
none I am aware of yet!
Data model changes
none
