When factions was first released, many people were whining about the free-for-all 12v12 (FPE) becoming 4+4+4 v 4+4+4 (now); but at the same time, it put some organization into the once chaotic ab from the FPE. So, I suggest splitting ab into 3 different arenas, based on how teams are formed.
Random 12v12 ab
Just like during the FPE, players enter the battle seperately & alone, and then are placed on teams of 12 players each. On the party list, everyone (all 12 players) are shown.
Arranged Teams 4+4+4 v 4+4+4 ab
Just like it is now. No particular changes.
Random and Arranged Teams would share the same arena lobby. Let's say you want to enter Random 12v12, you would simply hit "Enter Battle" without anyone else in your party. Alternately, if you want to enter Arranged Teams 12v12, form your 4-man party like usual, then hit "Enter Battle."
Now for the new idea:
True Alliance vs. Alliance.
Think of it as GuildA+guildB+guildC vs. Guild1+guild2+guild3. Basically you form your entire 12-man team with people from your alliance, and then go up against another 12-man team setup the same way. These 12-man teams should only be formed through guild alliance members. It's GvG, but on a 12v12 scale. This would result in highly organized strategy and very interesting battles to watch.
A few specifics, these 12-man teams would have to be formed either with a new "Guild Battle" option (within a guild hall in the alliance), or a new unique area shared by the guilds of the alliance (much like a community center). Although it would be implemented later, alliance ranking system, similar to the guild ranking system. And finally, observation mode for the high ranked 12v12 matches.
In summary, 3 new ab arenas:
random 12 vs. random 12 (FPE)
4+4+4 vs. 4+4+4 (currently)
alliance vs. alliance
Splitting Alliance Battles
Praetor