GNOME Apps in General: Relevant Art for Searchable Commands
Searchable Command Palettes / Heads Up Displays
Searchable command palettes or Heads Up Displays (HUDs) can be useful for both beginner and experienced GNOME users alike. Experienced users may prefer the command palette for its speed. Beginners may find the searchable command palette useful when trying to find commands.
There are a few existing implementations including Ubuntu's Unity HUD and Apple's searchable menus (accessible from the Help menu).
As for how to implement this in GNOME apps, I like the idea of having the feature advertised as a Help feature for the benefit of all users and with a keybinding common across all GNOME apps for the power users.
I'm including screenshots of some existing HUDs / Command Palettes.