There definitely needs to be a variety of tanks for the longevity of this game. As of now players think tanking ia boring and with only 2 to choose from.... vs dps.

I can see a dark Knight happening. Using hp to cause more dmg and aggro.

A caster tank will be truly unique

Samurais also makes sense as a tank due to using 2 handed swords + heavy armor.

I can also maybe playing as a garlean gunner as a tank using explosions, lasers and aoe machine gun