My idea is pretty complex but would actually be a good way to fake having an exterior view.
When you come open a door to any building, it automatically assesses where the windows inside are and puts a camera in the exterior world and quickly grabs a screenshot of the the view from that window. Now it has the "view" for the current time of day, etc... the view should be cleaned of all NPC's so only the scene is visible devoid of any other living forms in it. Now there should be a stock number of "people walking animations on green screen backgrounds" in a "outside view" Library. The game merges the live green-screen actors against the snapshot taken a moment ago, creating an animated faked external view that is rendered back from the window a ways so that if the player looks from different angles he still can't see the entire screen so the illusion isn't compromised. Since the game is actually rendering NPC's of that city moving about the streets from a large library of stock footage, no two viewing from the same window wuold have to be identical, making it appear "alive" ... or real.
The stock footage would have to be taken from a ground-level view and also from a 2nd-story view because of the differing angles looking down on the people as they are walking around. To create the 2nd-floor view, you would need to alter the background-wall and the floor plane's viewing angle in the outside-view window renderer. You would need two screenshots from two angles (one looking across the street at the background wall) and one looking down at the ground. These two snapshots could be mapped onto 3D flat planes respectively and rendered outside the window cell you're looking out of. From the 2nd floor, the angle would be shifted to an isometric angle, allowing a view of the background and street, and then the live-motion greenscreen actors could be merged in over the top, providing the illusion you are seeing out of the window down to the street below.
The images for all the windows are grabbed in the same transition it takes to load from the exterior world cell to the interior cell, so you won't notice it.
Then, no matter what building you went into, day or night, rain or shine, it would always reflect the current weather as when you went in, because the window animation controller could also control the weather outside, too. So if say, it began to rain, and there was a new view outside of it raining, then when you actually left the shop and went outside, it would really be raining because the window animation controller set it that way.
Keep in mind, the windows could be slightly warped (poor craftmanship) or slightly opaque to make it harder to see every detail clearly, to help sell the illusion should too much detail somehow compromise the illusion.
This would still have to be programmed. But only once. And then it would work across the entire system and for the future games also. If this didn't make sense in some way, please gently tell me why, I'll try to re-write it more clearly. Thanks...