Global community director Marcin Momot of developer CD Projekt Red confirmed on
Twitter that the medallion belongs to the School of the Lynx. There was never any doubt that the medal wasn't from the School of the Wolf, and its half-buried catlike features were just vague enough to implicate the School of the Cat and Ciri with it, but this medallion actually belongs to the Witchers of a very specific feline faction.
The School of the Lynx has a more tenuous presence in the Witcher universe on account of it
being largely rooted in footnotes and fan-fiction. The fact that it's seemingly at the heart of the "new saga" that the next Witcher game is planning implies that Geralt has indeed left center stage, but with the School of the Cat largely out of the theorycrafting picture, there's now less to suggest that Ciri will take his place as the lead in the story, and less still about what her challenges and motivations might be. So we're not quite back to square one, but we're pretty close to it, and we likely won't get more story details for some time.