Can you fathom how much it will cost to dig up the streets, lay fiber and fill them back in? Will cities even allow that, due to the impediment to the traffic?
It's been managed before for fiber deployments in northern Europe. I remember seeing a perspective on Ars Technica from Amsterdam, with a photo of a sidewalk tiles neatly removed and replaced without damage: http://arstechnica.com/tech-policy/news/2010/03/how-amsterda...
So, it can be done.