@2k Greg
Thank you for coming by and spreading the news.

No need to say it is a very exciting announcement.
Trying to figure out exactly what this means for modders. I do a bit of programming but have never done any modding. But follow the modding community regularly.
Does this allow the actual changing of the underlying rules?
Will this allow the upgrading of the AI's behavior?
In essence, yes, it will allow mods to perform deeper modifications, such as the one related to gameplay and AI. Actually it gives mods the ability to rewrite a part of the civ5 engine (half of it roughly, and the most interesting half from a modder's pov, the other one being the rendering engine and such).
Now there is a big catch: this is not modular, so if two mods each bundle their modified version of the dll, you can only use one of them (although you can have both installed). Also, those mods will likely not be available from the Steam workshop since they escape the little sandbox we used to be confined in.
For those reasons and for the example, while IGE could benefit of it to fix a couple of bugs and allow more features, I may not use this freedom so that you can still use it with other mods that really need that power. Or maybe I will submit a patch that dll creators may or may not apply to their own versions and let IGE detect whether the dll includes my patch or not, so that IGE can take advantage of my modifications when available.