I think if you reintroduced Scourge to the game, the playerbase would expect it to be a DoT and you would get complaints if it wasn't. If you want a new effect, it would be much better to create a new action name and a new animation that perhaps draws on the inspiration of the original without copying it.

The only real benefit that I could see in bringing back Scourge would be if you could implement it as a vampiric debuff that drained HP over time (with Soul Survivor giving you the remainder of the HP if the mob dies with the effect active). Or perhaps you upgrade the Carve and Spit/Abyssal Drain duo into a single high potency AoE with a drain over time effect. I wouldn't be surprised if that pair of abilities ends up being one of their upgrade targets anyways.

I don't really see the point in bringing back Power Slash just to replace Souleater. Especially since the latter is a signature action for DRK across the franchise. I miss DRK's speed boost the most out of all the gameplay changes, and Power Slash was always the slowest part of pre-Shadowbringers DRK. It was also the one move that good DRK players virtually never used, so it just feels wrong on a lot of levels. An additional combo action would be a nice addition, but the place to add it is after Bloodspiller.

While I think Oblation doesn't really have a great niche and would rather see it incorporated into a defensive upgrade, the chances of getting two charges of 20% DR Dark Mind on a 60 second recast seems fairly unlikely when you consider the likes of Camouflage. Unless they make a decision to just upgrade Camo/DM/Thrill/Bulwark together, which would be a waste of an expansion action on all tanks. The only mitigation move that I could see a case for upgrading is Dark Missionary. Just replace it with Runic if it has to be magical themed. Otherwise, just give us a Weapon Break style debuff that works on both damage types.