Here is a concept 5v5v5v5

lag

I think other games already have shown that such big fight don't really work well. 20 players is too many. However, I do believe that a 3v3v3v3 is possible and would be more balanced than a 2v2v2v2. Sadly, it would take a long time to balance this, like a really long time. Ontop of that, the UI isn't made for this and matchmaking would be a pain. I'd love to see the idea done, but it's definately not something that shouldn't be playtested a lot before it's released.