Civilization V is a Steamworks title (i.e., all versions require Steam). As such, I consulted the store page of Brave New World

The game is listed as DLC, and steam indicates that it only requires the base game to play.

In short, you should be okay to pass up Gods and Kings, though it is not clear what systems from Gods and Kings are reused by Brave New World anyway -- some of the previews on gaming news sites have indicated that certaing G&K features, such as 100 hit points instead of 10, are part of Brave New World as well, not to mention official screenshots from the Steam page (such as this one) showing a game with Faith resources.

This would mean, then, that if you will get most of the benefits from Gods and Kings except for the civs, relegating the expansion to a simple bundle of Civs and leaders, to those who already own Brave New World.

Civilization V is a Steamworks title (i.e., all versions require Steam). As such, I consulted the store page of Brave New World

The game is listed as DLC, and steam indicates that it only requires the base game to play.

In short, you are totally okay to pass up Gods and Kings, since Brave New World contains all the changes (espionage, religion, combat, etc.)

This would mean, then, that if you will get all of the benefits from Gods and Kings except for the civs, relegating the expansion to a simple bundle of Civs and leaders, to those who already own Brave New World.