Leadsled and all.
Lets clear up a misconception. There is no such thing as ICAO airspace. There is an ICAO classification of airspace in which certain levels of ATS are provided. It is up to each countries regulator to determine where each classification is used.
Each country has requirements that suit the number of users, amount of airspace available, geography, infrastructure, political restraints, culture and training. What works here is not necessarily suitable for another country. Same applies, what works in the USA may not work here, but if it was to work, the whole system needs to be implemented, starting with culture and training. Changing airspace should be the last step.