According to one of the art director's for the game, Human Revolution at one point was meant to have at least 5 different cities or main HUBs until it was trimmed down to just Detroit and Lower Heng Sha.
The biggest problem ended up being the amount of work needed to create each area to be unique and fill it with content ended up being too much work for the team and the game would have been delayed for an even longer time if worked on.
At least 2 of the other planned HUBs did get some work on them (Montreal and Upper Heng Sha) which is why they have some references in the game but the 5th HUB meant to be India was only in concept stage by the time the current game itself was finished in development.
None of the extra HUBs are expected to be future DLC though with the focus more on filling the gaps or side-quests in the current storyline.
http://kotaku.com/5837308/deus-ex-wa...be-even-bigger