I have a feeling tanks classes (marauder/gladiator) especially gladiator will expand into alternate tank roles.

The core skills of gladiator lend itself to tank by nature, the first combo you learn increases enmity same with marauder. Up until level 30 when job skills come into effect, all previous skills learned revolve around tanking. So how does that translate into damage dealing?

Unless SE revamps all the class actions or equipping a job stone gives alternate versions of base actions I don't foresee gladiator or marauder being anything but a tank regardless of job stone equipped.