It looks like there was an update to the two 'Changing Worlds' yesterday, because the changenumber (as can be seen by clicking on the app data and looking at the history) shows the revision. I don't know for sure what this could mean, though I'm assuming by default that it's a new version of whatever they're working on that they're uploading to the Steam database, so whatever they're working on, they're keeping it updated on on Steam. Gearing up for the Fall Patch to be coming up soon, perhaps?
Regarding new content, there also seems to be a Chinese language version of Civ V in the works now too (according to the Steam database:
http://steamdb.info/app/8930/#section_depots). Maybe Firaxis will release some additional Asian civs as DLC to coincide with it? Vietnam and Khmer perhaps? Either way, it's good to see that they still think it's worth doing more with the game.
I saw that before I saw your post, and my first thought was immediately "Vietnam!". And then I realized it was just a language translation. But, going into searching for that, it's so far only been included in an as-of-yet unnamed Steam Sub, made at the same time, that is restricted for purchase only in China, Myanmar (on a side note, I really want to see Pagan as a civ, perhaps with a UA based on City-State bullying to reflect their history of tributary states, but that's off-topic), Korea, and then Iran, Sudan, the Syrian Arab Republic, and ... Cuba? I have no idea, but I guess we'll find out soon. Also, there's an "Unknown Country", that is represented with a BU - and I don't know what BU could stand for, though my first thought was Burma (which would be redundant because of Myanmar already).
Anyways, yeah, that's my sleuthing.