D8: Multisite global module update ability

I have a D6 multisite with 20 sub-sites running from the same installation. In Drupal 8, it would be nice to have:

1. A "superuser" who has can (a) list all sub-sites and (b) have global access to them all
2. Can put all sub-sites in/out maintenance mode, without having to visit each one in turn
3. Can update one or more modules, and run the update script on all sub-sites.