Teams would require something like ventrilo or Teamspeak.
Three problems:
1. the need of a TS/Vent server
2. ppl who have issues setting up their client correctly
3. or do not even own a microphone/Headset
Teams without voice communication will have a disadvantage compared to teams which got it.
Sure in the end there are even bigger issues which might occure (e.g. latency, timezones), but we should at least sort out the ones which can be solved.
Next issue:
How would you select the teams?
Shall ppl be allowed to choose their teammates on their own or will they be randomly selected?
How about substitutes in case one of the players of a team doesn't turn up at matchtime?
What about adjudicators who admin the server, watch the game and take the screenshot of the scoreboard at the end of the match?
....
i could go on with this, but i think you got my point.
Whoever is going to host a GES community tournament will have a lot of things to take care of, or else the event will fail.