This question has been asked many times for different reasons. Any kind of end game DK's input would be phenomenal.
I feel that every endgame raiding guild is using a Prot Paladin over a DK for their obvious reasons. According to sims and logs DK DPS isn't as high as everyone else either. So if you're a high end DK are you just there to be there or do you bring actual utility to the raid?
That's not just add control, that's just in general. Druids can battle rez, along with warlocks both of which do much higher damage than DKs do.
Arenas are highly favorable against DKs.
So if you're a godmode DK, what do you bring to the table? Yes bring skill not the class but if your damage isn't high because numbers just won't back up the skill what are you useful for besides a raid filler spot?