I think that the discussion around DRK's GCDs is reasonable. As I said earlier, we have 4 single target and 3 AoE GCDs. Pretty much all of the action happens through oGCDs. I think that it's reasonable to want a second combo, but if you're introducing it at Lv. 100 it should be something more impactful and more interesting than the standard maintenance combo that most jobs copy paste over at Lv.50.
Complexity and synergy are buzzwords that people throw out there frequently but don't carry any meaning. When you talk about the 'weight' behind hits, that's by and large a hitstop effect - WAR's fell cleave looks more impactful than Bloodspiller, which is why it feels more satisfying to use. Decimate doesn't, which is why Quietus is on a more level playing field. Pretty much all of RPR's animations use varying degrees of hitstop, which is one of the reasons why the job is still overwhelmingly popular despite not being FoTM. I think they realize this and we'll start seeing a lot more moves designed with hitstop in mind.
Pretty much every iteration of DRK has by and large been about unloading a swathe of oGCDs under burst. Part of the reason why Salted Earth is sitting at an odd 90s is just because they don't want to overload you with oGCDs. It's actually easy to make it even more oGCD intensive, all you need to do is increase the rate of MP generation and reduce the potency of Edge/Flood accordingly. But I don't think that would make the gameplay more fun. There are also limitations on how much you can add to the resource management part of the job without simply adding more resource bars. You can only have one on-demand action per resource (for single target and AoE). You can sort of work around this by doing something with the 'Dark Arts' gauge as I suggested with making a second resource-gated combo, but all that does is move DRK into being a three resource system job. Exchanging resources (MP for Blood) is a nice idea, but all this actually does is surreptitiously increase the rate of resource generation, which just translates into more Edge/Bloodspiller spam.
In short, none of this is really new ground as far as discussions go, but most of the changes that you could make would change the job less than you might think. I think a second combo could be really fun, given our paucity of oGCDs. If you did that in 7.x, you'd probably have to spend most if not all of our three new expansion actions to do so (two for single target, one more for AoE unless you pushed that back to 8.x). If you were going to do that, it had better something more interesting than Eye or Goring. It'll of course have hitstop. I think the best way to do it is to actually use Dark Arts as a third resource.