I dunno. I am certainly not against a Great Sword DPS, but for the same reason everyone else has stated, the game already struggles with role identity... not to mention the game was designed specifically to have class weapons represent that identity.
I guess what I am saying is there is no written rule against it, I certainly wouldn't be critical of the addition, and if they were creative with their design, it certainly could work...
But at the very same time, I strongly doubt SE would ever go that direction unless they were truly out of ideas...
Personally, I have been waiting and hoping for Gambler. Not only would the concept allow for them to go in any kind of direction, but they have past history with Setzer and other gamblers in their games. The gold saucer and Manderville's give the class a great foundation. Dice rolls, slots, and more.
I think it would be great fun and a awesome idea... But considering the very concept of the class and personally I would think it would be about 'chance', that would be directly opposite of recent 6.1 game design choices in removing variance and rng out of class game play, and maybe not pan out.
Certainly not a greatsword user either...
Though I suppose gambler could use a whip. Dice may be too simplistic and not ideal for weapon design, and a deck of cards shares the same problem, plus gets close in theme to astrologian, even if completely different type of cards.
For another greatsword user that is specifically dps, I think the idea (that others have touched on here) that would be the best, would be a berserker type of class, or something like Noctis does in FFXV, where the weapon type is actually 'multiple weapon' types. A greatsword just being one of them. A berserker could just sort of pull out desired weapon per move of the moment, almost like a weapon collector/Gilgamesh style warrior... Or more mystic/sci-fi like Noctis did with drawing them straight out of the air.
I fully admit to maybe enjoying a pure greatsword dps more... But I think it more likely SE introduce a greatsword dps through an idea like the above, rather then just plop in a 'SOLDIER' like pure greatsword dps class. There would need to be further differences from DRK then simply gothic/darker move set and doing dps rather then tanking.