Technocactus
Lurker
No, there won't be any fan-based mods but there will be mods made by the games companies and in Oblivions case the add on Kinights of the Nine will be available for free on the PS3 as opposed 2 (from what i have heard) the 10 dollers you have 2 pay for the Xbox360 version. Which means that civ could also make mods in this way as well.
But particularly for a game like Civ, the modding is an essential component. Civ is a lesser being without the capability for mods.