Light from panel is diffuse; it can't project rays, so will not look like daylight.

Perspective of view always totally wrong.

As screens age they'll drift or fail and not match each other, looking very fake.

No actual window is a channel for the view outside, so once placed, no one need ever further decide the view. The simple possibility of changing channels is destructive to the idea of a window.

But other than totally destroying the idea of reality, fake windows will be very "realistic."