Of all the different groups of willworkers that wraiths have to deal with, the Technocracy would be the best bet to strengthen the Shroud. While it would take a lot of doing - maybe more than they'd have time to set up for - there's no one else who could muster the kind of personnel needed to pull such a thing off worldwide.

There's a good chance that a lot of their people would be fried by "feedback" in the attempt, but this is the sort of thing that they're there to try and prevent, if they can. At the very least, they'd put up a valiant effort to stop it all from coming down, and might at least buy some valuable time. And you wouldn't have to worry about them trying to weaken it, instead - what would that prove?

On the opposite side of that coin are the Nephandi: twisted and destructive Mages who serve the same Malfeans that the spectres do, and may already be in cahoots with any or all attempts to raise the primal darkness. The good news is that, during the Great Maelstrom, their ability to communicate with their masters is dampened, thus limiting their usefulness. The bad news is that their standing orders are usually to do anything possible to help the home team, and bringing the Shroud down at a critical moment would definitely fall under that category.

There's also the Euthanatos and the Dreamspeakers, whose understanding of entropy and the spirit realms - respectively - could be useful in stopping this catastrophe. Whether their irregular and ill-allied inner factions could all get together and face a greater threat, much less all agree on what's to be done, is another question. And there's always a chance of some of their number actually making things worse, somehow.