Although we have yet to see any class tuning changes in 9.2 I wanted to take this opportunity to bring up some areas to look into.
Damage/Scaling
Across all three specs damage has either been lacking (blood) or not scaling too well (frost/Unh) so this is the first thing I would like to see addressed.
Frost and Unholy both do respectable damage during CDs (breath/Army), but offer little outside of them and fall behind, whether or not we see flat aura buffs I would not be opposed to targeted buffs to abilities like Frost Strike/Death Coil to bump up damage outside of CDs.
Blood needs help in damage accross the board, a 10-15% aura buff + an additional 10-15% for Heart Strike, Marrowrend and Death Strike for ST
Conduits
Another issue with DK is the scaling of conduits or the benefit of additional conduits. Everfrost and Eternal Hunger were great first conduits, the rest of the conduit options offer very little. Blood has no good conduits, one was so bad a 600% buff in 9.1.5 wasn;t enough to make us even consider it.
Frost
-Accelerated Cold gives 10% RP generation instead of CDR
-Eradicating Blow: Killing Machine increases damage of yor next obliterate by X%
-Unleashed Frenzy: Increases attack speed in addition to Strength.
Unh:
Convocation of the Dead: Bursting a wound reduces CD of Apocalypse by 1 seconds fixed, Wounds deal 10% additionnal damage scaling with ilevel.
Embrace Death: Death Coil deals 8% increased damage Scaling with ilevel, Sudden Doom quadruples this benefit.
Lingering Plague: Virulent plague deals 10% scaling with ilevel more damage and has a chance equal to criticial strike chance to erupt as if the target died.
Blood
Withering plague: Scaling increased by 25%
Debilitating Malady:Now also increases Blood boil damage, Duration increased to 12 seconds, stacks twice instead of 3 times for same buff.
We can also look to talents as many are never used due to undertuning or poor design, I leave those changes for a 10.0 type patch but all the above should be at least considered going into 9.2.
Thank you for reading and consideration.