The higher authority that would never let the new owners re-skin the dungeon in chrome and laser pistols.
The Syndicate appears as a limit on what the new owners can do. Working through what The Valtay takeover means, Mordecai argues that the fantasy theme of the dungeon will hold: a Valtay-style floor of androids, hovercars, laser pistols and mechanical death machines would not make sense, would not go over well with the fans, and — decisively — the Syndicate would never allow it, nor would the AI.
That places the Syndicate above the corporations squabbling over Borant, an authority whose consent shapes what the game is even permitted to look like, whatever the ownership stake says.
The overarching authority whose rules constrain how far a new owner can remake the dungeon.
Also appears in books you've already read — spoiler-safe to their endings: