Managing resources shared between plugins (keybindings, markers, etc) is an acknowledged issue that hasn't been solved so far. Thats why its recommended that plugins do not set keybindings by default, leave it to the user to de-conflict, they are hopefully smarter than plugins :)
On a practical note, the order that plugins are loaded is undefined, and the user can select to not load a plugin at all, so plugins can't rely on other plugins since they may not be loaded at the time they are needed.
Better would be to try (again) to get a more general solution to the shared resource problem, or at least keybindings, built into Geany.