Slitherine

Ruins. Right now my tanks can blitz through the city hexes to come out fast on the other side and black the enemy from crossing the roadways. This is to easy. Moving a tank through a bombed out city should be very slow, at least for vehicles.

By adding a version of the city hex that behaves more like forests or swamps, it would be easier to simulate the effects off artillery and air-strikes on a city.

Interesting and very good idea.

Might be something for the future, I see little chance that a new terrain type can make it into a DLC.

Great idea, but shouldn't it change as the game goes along?

This also should occur in any city you actually assault, such as Sevastapol, Moscow, etc. The terrain could change if arty, air or ships strike it 2X and the same if troops actually fight in the city for 2 turns. The terrain could change to a rubble look much in the same way a bridge would get blown up in PG2 (another feature that should come back ) Of course, I do not write 'em, I play 'em. Not sure how hard it would be, but it sounds like a cool feature. Just thought of it as I assault Sevastapol again...

Might be something to consider, but I wouldn't hold your breath. Tanks and other non-infantry units are already quit vulnerable on city tiles, reducing their mobility as well might be too much.

I wouldn't be too fussed if the rubble affected combat stats and movement but it would look really good IMO if, as suggested above, a number of ground assaults, artillery and/or air attacks changed the overlay from buildings to rubble. I wouldn't think that would be too difficult to do, but then again I'm not a programmer.

Any change of that magnitude won't be a part of just a DLC. One of the themes of the DLC is to create the maximum amount of content with current features.
Keeps production time and cost down, which is why we're able to produce equal length campaigns at a fraction of the cost of the main game.