So DRK will be mp based

[Risvertasashi]

Like, you have a 1000mp pool and increase 1 stack of this "aetherflow" would cost like 600mp? It's interesting. Managing mp and using the stacks to use some skills... sounds promising.
But something tells me it will be like a bard's song... While you sing it, threat will increase, mp will decrease and you gain access to dark powers. And you can cancel the 'stance' anytime to save mp.

I was thinking more like "Spend X amount of MP to get 3～5 stacks of Darkness™". Then you spend these stacks on The Good Stuff™--your most powerful (but not only) abilities for threat generation, mitigation, or damage if you're good on the first two counts.

Of course, this is all just pure speculation. Your take also sounds interesting!