The most current example I have of the Overton Window in action is Berlin passing a 5 year rent freeze law. Berlin's rental prices have been going up dramatically. And, there are more and more private housing owners.

But, it so happens that the German constitution still has terms in it about the government being able to appropriate privately held housing from any entity that owns 200 or more units. Activists in Berlin starting talking about this law and suggesting its use. Where before private interests were against any sort of rent freeze, a 5 year rent freeze was agreed to, when faced with the much more "radical" option of having the housing appropriated. So, the activists "shifted the Overton Window".