Please remember that these are rumors.
Via Beasts of War
You will be able to buy terrain. This means that alongside your army you might be bringing some of your favorite terrain pieces with you. Especially armies that can fortify ruins or only get stealth in forests and jungles, this could be invaluable.
Other rumors also bring about mysterious terrain elements. Terrain, you just are not sure what will be there until you enter. I imagine it would be like not knowing if those ruins are dangerous or just difficult until you get into them.
Also are the possibilities of something like Drop-Shipped Terrain. That could be dropped in during the battle or before and scatter onto the field. Mines or some other things might fit into a category like this.
Last but least, we have "Terrain on Fire". You will be able to use flamers to literally set terrain on fire. To add to that, the terrain will burn for some random number of turns. We don't know how this will work or how long it will be in effect. However it does sound like its not an automatic thing to set fire to the ruins. Perhaps there is a toughness or armour value for different ruin types the flamer must reach in order to set the ruins on fire.
To me this just adds to the fun and cinematic value of the game. What do you think?