Replace a window with a digital display, put one or more cameras on the back of it, then apply transformations to the outdoor view: make a rainy day sunny, make a short day longer, or replace a brick wall with a stunning view.

Difficulties:

• parallax: the illusion is ruined as you move around the room unless the display tracks your location, a la Disney/Lucasfilm's "Stagecraft". And I bet that's patented.
• further, even Stagecraft can't alter the view for different people separately

It seems like what you really need is a smart hologram? Something that can alter or override the transmission of light at all angles. Something that did that would not need to track the viewers' locations. It would also massively complicate the computational task of updating the view.

Looking Glass Factory has a holographic display that might work: https://www.youtube.com/watch?v=EMUdmE0lKIU Though it's not currently large enough for an entire window, at least not a very large one.

Light Field Lab also seems to be working on something similar