It seems players can assign a hero to a sanctuary, just like shown above.

Steps to Reproduce

1. Heroes Screen (F6 iirc?)

2. Select a Hero

3. Assign to a System

4. Now you can choose sanctuaries in the list

According to the user who reported this bug...

• Hero skills affecting systems do work
• XP of heroes does increase
• Quests requiring players to assign heroes as governors do count heroes assigned to systems.

+ Some even said you can do the same at the Empire Overview (F1) screen.

* Reported from Korean ES2 Community Users

Wait, is that unintended? I assumed that was working as intended :x

No, it was introduced in previous patch before current.