Since you joined our clan 11 hours ago, you probably found the best place for teamwork already.
As you say, voice communitcation is a key element for coordination, which mumble provides.
The problem with specific roles withhin a team is not a new one. And it is proven that people are the very best at something if they always do the same job again and again. But that system is very difficult to implement into Zero-k.
Lets imagine we have the following positions:
In a 4v4, you would be able to stuff every position. But 1 player to hold the front against probably 4 attacking players from your enemy would resume in a relatively short game.
In a 10v10, where you could determine 7 frontplayers, the system could probably work.
So the role-system is highly dependent on the number of players in the game. This would force certain specifique players (Air or Eco) to play another role from time to time, which would go against the rule of always doing the same job.
So this idea is only viable a very small amout of teamgames.
A leader in a team is something that can workout, independent of the number of players. But you must consider that in most games, most of your teammates won't use mumble. Even as the largest and strongest active plan, we most of the time are only 4-5 guys in our team, out of 10. So the leader would only command a very limited amount of the teams ressources.
In mumble clan we have many high ranked players. Therefor in teamgames, we almost certainly have 1-3 noobs which are close to uselessness. With the additional troll that leaves 6 out of 10 players to fight the enemy. So these higher ranked players are forced to take responsibility at the front lines in order to keep their team in the game.
Therefor they often can't go for Air or Eco.
(I'm running out of time... i need to leave xd...)
When you gain more experience you will also realise that only a very limited number of players would be capable to fullfill the role as a leader, since it needs an good overview of the situation and the map. And these are all high ranked players...
So all of these reasons combined make it very hard to use this system with roles.
In mumble, you will realise that the higher ranked players often take the lead by giving advices or coordinating attack/defense. And i think that is as far as it will go. Also mumble is lead in a democratic way, also during battles.