I want her to be a sort of larval Borg queen. It's a common fan-theory that Seven was being groomed to replace the queen. But that plan was obliterated along with a portion of the Borg transwarp hub in the events of Endgame.

Looking at the "facility" that appears 1 minute into the trailer, I really think it resembles a Borg cube. The upward shot featuring the "5843 days without an assimilation" sign (almost exactly 16 years - not sure if that's relevant yet) features Romulan guards and two things that look a bit like alcoves. They then cut to a shot of people standing around in prison uniforms of various species.

My guess is that these people are former drones, cured in the de-assimilation theater shown at 57 seconds (same aesthetic, also guarded by Romulans).

Not sure if they'll do it, but I think it'd be cool if she was being groomed to be the next queen after Seven made it back to Earth. Then once she gets mostly de-similated, she seeks out Locutus.