WMG for "Doctor Who S35 E7 "The Zygon Invasion"".
The box looks a lot like The Moment! Could the Doctor have left her with UNIT? no way he could return her to Gallifrey. When she appears, it will not be as Bad Wolf Girl, but as the other Osgood. She may have already appeared without our realizing, helping to guide our heroes to a solution which does not require activating her, just as she did in the 50th.
- Jossed
So what if the reason the next episode is called "The Zygon Inversion" is because the 20 million individuals who now think they're a new generation of Zygons are actually humans, who were given Zygon memories and body-print alternate shapes as sucker-coated aliens, then re-settled outside of Britain, while the real Zygons remained sealed up in stasis bubbles? They would live like Zygons for a year, then have their original identities restored, but with the memory of being a refugee alien in desperate need of a home, to whom Zygon bodies and habits were perfectly normal. The real secret plan for the peace was that, over the course of decades, millions more humans would be temporarily given Zygon identities, gradually teaching the human race that Zygons are not so different, until every human on Earth had lived a Zygon's life. At that point, they'd no longer have any innate fear of Zygons, only of being exposed as one; to finalize the bargain, the transformation-technology could be suppressed for both species and the pod-bound Zygons could emerge and live alongside humans as their real selves.
So the Osgood Box doesn't contain the means to destroy the Zygons, but the means to negate the human "Zygons'" transformations en masse. If it's found and activated, the rebels will discover that they've actually been humans killing fellow-humans all along.
- Jossed