Please enlighten us BIK
Once all the aircraft know where everyone else is and they can seperate themselves, and reading between the lines, when you see no need for ATC (or "ground based radio operators" as you call us), who decides who changes level, who diverts off their track to let the other guy stay at his preferred level, who volunteers to hold while he waits for the other guys who got there at the same time to make an approach. Even with ATC when you tell two company aircraft that one of them has to change level and ask them to decide who it will be, alot of the time it ends up neither want to change cos they both have good reasons to stay at their preferred level. That is one of many of the reasons why you do need a third party even in Enroute Airspace.