Schema should show descriptions and possible values for fields. Maybe it should even have some kind of entity-relationship diagram for the tables.
I've added a subtle question mark icon next to the Database schema title in the compose query view:
Clicking the question mark brings you to Database schema documentation for the public data dump and SEDE
The changed Editor.cshtml can be found in Pull Request 108. This is now deployed and live in rev 2020.12.13.80.