Was does airspace ownership need to be fixed? Why can't it float between centres depending on the time of day. Most controllers I know don't like the night shift (I don't and who can blame them).
The current feudal system of upper enroute air traffic control in Europe is a joke.
Confine the military to small areas beneath and/or clear of the main airways and consolidate the upper enroute air traffic control to a few centres taking into account technology and time zones. Probably won't mean fewer jobs overall especially if there is an expansion of civil areas.