I was trying to add a convention whereby the InputGestureText of a MenuItem can also be used to trigger its attached message.
<MenuItem Header="E_xit" InputGestureText="Alt+X" cal:Message.Attach="Exit" />
Would have the effect that pressing Alt+X will call Exit (if CanExit is true). The trigger is attached to the root visual so that it becomes global.
My very hacky implementation of the trigger can be found here: http://github.com/royjacobs/Lux/blob/master/Lux/GestureTrigger.cs
I was also thinking about just porting the VM-based menus from Caliburn Shell Framework, though, but I just wanted to understand the reasoning behind the 'one convention per type' limit.