I just watched the Firaxicon 2015 panel called Civ V Retrospective: The Complete Edition. It was a great, exclusive look at the history and development of Civilization V! Find my summary of the presentation at the Civilization Wikia's Facebook page. :) Here's the full video:
And here's a few screenshots, demonstrating some of the various topics that are discussed:
The first prototype of the fog of war
From the blooper reel: huge horses!
Evolution of a name of a game