So, is that a dagger? (In the new concept art.)

[Ramsey]

Gladiator > Thief?

The only class in game that uses daggers right now are gladiators.

This is inherently impossible due to the way Gladiator is structured as a class. So much hacky skill-changing would have to occur that it wouldn't be worth it to not just create a new class. Gladiator has no interesting DPS combos and all of its skills are focused on enmity generation and reducing incoming damage.