What can and what cannot be said is in constant flux. For every newly introduced taboo other taboos go away. It's conceivable that the Overton window narrows on

What can and what cannot be said is in constant flux. For every newly introduced taboo other taboos go away. It's conceivable that the Overton window narrows on 'community scale', but I don't see any evidence for that. In some communities the Overton window is shifted massively in one direction, but not at the expense of width.