Don't hold your breath for any global changes
On average it takes SEVEN years to process a change thru ICAO, with only one change in recent times going thru in about 3 or so.
The mass of the ATC system in North America and Europe would make even discussion on major change very difficult, especially if they don't see a problem.
A risk assessment on a major change might probably conclude that the risks involved in the change alone are not worth the change? As a result any changes would have to be piecemeal and as a result would take a lifetime.
Like it or not the menu of airspace classes is what we have and from an Oz point of view that is the choice, with only perhaps minor procedural changes etc.