The post-physical transition path Tagg secretly began, the clue that ties the Dream to the Reavers.
Baroness Victory singles out the most interesting fact of the whole political mess: that Epitome Tagg decided to secretly start moving toward the post-physical form path. She can see why he would hide any association with the Reavers in the galaxy over it — the Reavers are the faction people fear will shepherd everyone toward singularity.
The path is also what makes Tagg's current predicament legible. He is already partway out of a body, riding Louis's organs, and demands a grown replacement on the Eighteenth Floor with a brain implant to be finished at the Reaver Castle — the machinery of a transition Fopsy, his own adjutant, claims he never noticed.
The secret transition Tagg pursued, explaining both his hidden Reaver ties and his bodiless state.