It's hard to say what the result will be without seeing in-game footage. With 15 jobs, it's difficult to showcase everything, at least if you want the live letter to finish in under 10 hours.
The job reveal does actually provide a fair amount of detail, however.
In the video, we see:
Darkside -> DA -> Blood Weapon -> New Move -> Plunge -> HS -> DA -> Carve and Spit -> SS -> Soul Eater -> Grit -> Defensive Cooldown -> Reprisal -> DA -> New Move
When Blood Weapon is activated, the new DRK gauge starts increasing, at a rate of 3 units for every auto attack or ability (similar to the trigger for Blood Weapon MP ticks). Dark Arts does not cause a drop in the gauge, so it's probably still tied to MP. Both of the new slash moves have Dark Arts prior to their use. In addition, they also consume 50 units of the new DRK gauge. Soul Eater independently appears to give you 10 units, at least out of Grit. When Grit is applied, the DRK gauge stops increasing, possibly because the Blood Weapon effect is removed.
The defensive ability in the video looks like Shadow Wall at first glance, but the animation is different. It's actually the same animation that the DRK does on their targeted "Cover-like ability" in the Stormsblood Benchmark. This suggests that not only can you use it on another player, but you can use it on yourself as well.
Reprisal is interesting. It's used without any kind of a proc. It's hard to tell whether this is the new shared role action, or if they took the animation for Reprisal and applied it to a new DRK ability.
On the whole, it looks like we'll have another layer of resource management to potentially set us up for some big damage moves.
It's hard to tell what the end result of these changes will be without a complete ability list. Low Blows becoming shared doesn't just affect DRK, as WAR has lost Brutal Swing as well. Reprisal becoming shared compensates for the loss of the Storm's Path debuff on WAR. You should also note that the new gap closer on WAR costs 20 IB to use and is 100 potency, although it's on a 15 second shorter recast. There are trade-offs everywhere, and the changes look very fair for once.
I think the most important part will be the raid debuffs. WAR still has slashing, but it's been switched around to Maim instead, with SE taking over the role of self-buff. Without having the chance to see either of PLD or DRK's combos in action on an in-game target, we really don't know what their debuffs will be. We also don't know what modifications have been made to existing abilities yet.
I will say that every tank actually looks interesting to play this time around, which is definitely a step up from Heavensward.