Python is a programming language of sorts. Basically think of it this way: XML affects the values, like changing a warriors power from 2 to 3. Map editing affects the placement of things, and DDS editing affects the appearance of things.
Python, on the other hand, is far more potent in how it can affect things. Depending on how much of the inner workings of the game they exposed(something I haven't fully investigated yet), it could potentially change even the fundamentals of the game, for example changing the combat system to have 2 values like Civ 3, allow you to make cities buildable in the ocean, or pretty much anything else. If they exposed a significant amount of the inner workings of the game, you could end up with flying cities, bridges built across the sea, or even space colonization. The only catch is you would actually have to program these changes, blow by blow, rule by rule, no shortcuts of any kind.