I've actually discussed this with some of my FC mates - in FFXI dark knight was known for two things

1) Great Sword
2) HP used for Damage moves/Bonuses

Right now we have classes that use MP for damage (mages) or MP for damage bonuses (brd) - or TP for damage (mnk, drg, so on).

I would love to see them introduce dark knight as a great sword DPS that uses HP for damage bonuses/moves. This would mean you could make the job fairly easy to execute massive dps... but only as much as the healers can heal you. MP and TP could be used for triggers on the moves (which then consume HP based on damage). Basically they would be a class that can self suicide really easily... but deal massive spike damage. A dead dps is a useless dps though in most fights.