Rod
King
Modability: With unprecedented modding tools, players will have unlimited options for modifying Civilization V any way they like.
source
This doesn't mean anything. They released the source code for Civ IV. There is NO Tool which can compare in power with this release. However only a small minority of modders was able to handle this gift properly and therefore many projects died due to the lack of either developers (code experts) or graphic specialists. But the projects which had either or both became the best mods ever made for Civilization.
RFC, FFH, HoTK (History of the Three Kingdoms) ..
Hence in Civ 5 we might expect a powerful modding tool which will be easier usable for a larger group of modders. However if the tool will give only access to the variables, but not to the mechanics and (if this is the case) they won't release the source code then a project like FFH would be impossible and just imagine RFC without stability and other new and non-Firaxis features...