Yoshi said somewhere that he wanted DRK to come from GLD. I'd imagine they would give a DPS based combo finisher to Riot blade, that increases damage dealt by 20% or something, and then make a bunch of HP sacrificing attacks. Subs would be LNC for sure, and then either Archer or PUG or maybe even MRD(with berserk as a cross class skill?). I think it would need a lot of work to make DRK come from GLD though.. they have too many tanking abilities.

If they could change GLD abilities to have different effects when classified as a DPS it could work. For example, Rampart could change from 20% defense boost to +20% crit boost, and Rage of Halone could change from increased enmity to some kind of damage over time effect, or slashing resistance down.