User blog comment:ExSturminator01/Mass Effect 3 Predictions based on ME2 hints/@comment-1894157-20100301143914

@ExSturminator01: If I understand it correctly, dark energy can be manipulated to create mass effect fields by passing an electrical current through element zero. This is used on a large scale to allow ftl travel, but also on a smaller scale in biotics. I think the explanation for human biotics is dust-form element zero exposure in the womb gave them their biotic potential, and that this eezo can be manipulated by their electrical impulses.

I agree that this doesn't fit the reaper's MO, but then they've been using the Citadel as a hidden mass relay tactic for a long time. Now that they are stranded in dark space they will need another way to get back to the Milky Way because normal FTL drives would not be feasible. Maybe this was an attempt to create a wormhole or maybe even a new mass relay that they are trying to link to the one they normally use to get to the Citadel. We still don't know how mass relays are constructed - only that the Protheans were able to reverse-engineer it.