Ok, so just doing some brainstorming here, we all know there will be a 12th class - blizzard introduces new races and classes to keep the cost of low level items somewhat relevant and to make you play more. And Blizzard always intoduces hybrids so there's more freedom to people/more people able to tank or heal.
Now, since only hunters use bows/crossbows/guns and only rogues use agi daggers I think the new class might/would be good to use those.
So I'm thinking one talent tree will be DPS, and ranged hunter weapons, another will be tank and use a dagger and shield or just daggers, and a third will be intellect healer. Now, there are only two mail users, and one int mail and one int plate user, making me think the class will use agi mail in tank and dps specs and int mail OR plate mail in healer spec, having some sort of ability that automatically upgrades the armor value of any mail when used in healer spec, and being able to only use plate in healer spec, and having a hybrid mail/plate specialization in healer spec.
And as an added bonus, since only 3 classes/8 specs use strength, maybe the tank and dps specs also use strength, making them use str gems and trinkets and enchants, and having an ability that automatically converts non-gem/enchant egility on their armor/weapons to strength.
Like I said, maybe blizzard won't do this, but I feel like it would be the perfect solution to our problems.