Scanning and other forms of automatic content generation do not replace manual 3D modeling and texturing; just as cameras did not replace painting and sculpting.
Personally, I'm more excited about procedural generation than any of these other ideas. Programming seems to be the most powerful tool humans have ever devised. Why not apply it to create art?
If you could use automated scanning (or other means of observing the real world) combined with procedural content generation, that could be huge.
Buildings that look and feel like buildings because they were procedurally generated with a deep understanding of how buildings actually exist? Yes, please!
Usually you want to deliberately distort the real world significantly, to reduce the distances by an order of magnitude while keeping the 'feel'.
You don't a GTA-style game to take 40 minutes to commute from one place to another; so you want to keep the noticeable landmarks but cut out huge parts in the middle. You want wild alley chases to be possible, so you make many places connected and cross-navigable in patterns that don't occur in real life. You want to drastically increase density of 'interesting' places, not mirror their density in real life; and leave out endlessly repeating miles of similar suburbs or apartment blocks.
A false world that's at least informed by the real world can be more compelling than something totally abstract.
I'll always remember riding around in stolen cars in Vice City, a city that, while not real, is lovingly informed by the real world. If someone made a procedurally generated Vice City that I could drive through forever, yes, please!
I sort of agree with you. I haven't been to Florence, but after playing so much Assassin's Creed 2 I recognized real photos.
On the other hand, if it's procedurally generated, it's not informed by the real world. There's a reason even procedural generation needs game design, you can't just throw random stuff together and expect it to be coherent.
Or it could take chunks of the real world and randomly sprinkle them through the game world. It would get boring fast.
Have you looked at google maps 3d view lately? That's all procedural, and the emphasis isn't even on photo realism. It's not difficult to conceive of a drone that does scan and take high res images and software that stitches it all together later.
Personally, I'm more excited about procedural generation than any of these other ideas. Programming seems to be the most powerful tool humans have ever devised. Why not apply it to create art?