Back in '65 that was the whole idea behind Eurocontrol. A logical progression into the jet age (as it was back then), scuppered by lack of political will / agreement. An idea that's a lot lesslikely to fly (no pun intended) today given ANSPs as private entities with shareholders and ATC being 'run' as a business. All the market forces are working in the opposite direction with everyone wanting their slice of the pie. Most probably, MST in its' current form, is time limited.