Until recently, every version of Oathseeker, the protection paladin sword that comes with the shield Truthguard (the shield being the half of the pair with its own unique properties) has looked like a simple re-color, regardless of which model you choose for your shield. But that seems to be changing, and the really exciting thing is that it appears that one of these models will be a flail.
In addition to the fact that the flail seems to match the "Holy Fire" Truthguard model, another piece of supporting evidence that this goes to Tankadins is that it recalls our Diablo III equivalent - the Crusader. In Diablo III, each class has its own unique weapon type in addition to unique armor types (actually, Crusaders are the exception here, unless you count Crusader Shields as armor instead of weapons.) Crusaders get Flails (in both one and two-handed varieties, though they have an optional special passive ability that allows them to wield a 2-hander with a shield.)
There is one logical problem with using a flail as a tank - namely how one parries (though I suppose you could kind of swat the enemy's weapon out of the way - it would require much quicker reflexes.) Still, this is a type of weapon that we've never seen in WoW, and it would be cool to let Protection Paladins use it.
EDIT: Here's video of the Flail in action: