I'd do it! Great idea!
This is just a total 'make it so' idea. I love DA -- I occasionally take a level 50 character in there and zoom around just freeing ghosts from the BP ceremonies, and I think it's a crying shame that there isn't a good, solid plot arc to be found there. The phasing tech would be the perfect solution to the problem of how to finish the arc.
Arc#314490: Zombie Ninja Pirates!
Defiant @Grouchybeast
Death is part of my attack chain.
Yeah. I know this won't happen. But random and long-level-range covering thought:
Three-phase Dark Astoria content.
Phase 1: 25-35. Dark Astoria "Now."
Yes, this overlaps with Croatoa. There's reason for it - with some minor mentions from Skipper and perhaps Kelly Nemmers, a link can be created between Croatoa and Dark Astoria. "Whatever's going on here seems to have disturbed things over in Astoria. Talk to...."
I know the lower end of this range isn't exactly hurting for content, but it's level-appropriate for the mobs that are in there. (The BP end up disappearing for a while as it is.)
The "Now" explores spiritual unrest, the BP's efforts to bring their gods in/wake the sleeper, and the COT's efforts to keep him bound (as well as find out just what the Tsoo are looking for.) Ending with a quick task force.
If you don't have it already, the ending makes sure you have Ouroboros unlocked. (No, I don't really have "story arcs" set up for this.) DA doesn't change at this point.
40-50: "Then."
This is through Ouroboros. Why? Because the region that's now Astoria/Dark Astoria has gone through upheavals like this before. Visit the one in the 50s. Get sent back farther - because something's upsetting the flow of time, trying to break through. This explores the area and a bit more of the BP.
Ending, quite likely, with a cutscene. A very dark one... where some figures emerge, just before you're flung back into the present.
50+: "Future."
Must have Incarnate powers unlocked. (I'd even go so far as to require Judgement/Interface, not just Alpha.) Why?
Because you have the power of a god. And you're about to go face the Pantheon on their home turf.
Gives appropriate Incarnate-level rewards (2 arcs, each have at least an Emp merit, Astral for major accomplishments, threads will drop.)
At the end of this, Astoria is reclaimed. No fog (unless you exemp down) except (like in the Croatoa missions to investigate spirits) in one or two very localized spots. COT still lurk here and there, but they're uninterested in you - or don't want to challenge you. The ghosts are at peace, and we have real civilians again.
I haven't generally been a fan of "Clearing the fog permanently," but given the phasing (and the elimination or severe weakening of the Pantheon that would happen at 50+ with the Incarnate arcs) the "clearing" would be an ample demonstration of your power as an Incarnate (and a heck of a "tangible" reward.)