I personally hate global menu bars. They do not work with focus follows mouse. The way menus currently work is fine for me and I would not want to lose that to, IMO, a much worst system. Any global menu implementation would need to be able to be disabled and better to have it off by default. And I would rather see effort in developing other features personally - though mostly as I would never use this feature.
I have more then once gave up on pressing up, hit ctrl + c to reset only to see the command I wanted briefly flash up as I am hitting ctrl + c