[Baertram]

Cannot create you such addon atm but you can try to add a slash command /esc.

The keybind should call SCENE_MANAGER:OnToggleGameMenuBinding(), or the function by ZOs is: ZO_SceneManager_ToggleGameMenuBinding()
This is the keybind that ZOs defined as not rebindable:

<Action name="TOGGLE_SYSTEM" rebindable="false" allowOnInputModeChange="true">
                <Down>ZO_SceneManager_ToggleGameMenuBinding()</Down>
            </Action>

Not sure if we could overwrite this, but I doubt it.



Try to add this to any addon you got, at the EVENT_PLAYER_ADD_ON_LOADED callback function:

SLASH_COMMANDS["/esc"] = function() ZO_SceneManager_ToggleGameMenuBinding() end

Not sure if this works as ESC in all circumstances, like at an interaction -> ESC -> Close interaction, but it should


Edit:
I've tested to add a new keybind for that and it works.
I'll add that to FCOChangeStuff

Edit2:
Both added