I've always loved the battlefield series, but I always found it al little strange how the effects of enormous bombings, tank duels, and various other explosive situations, fail to effect the surrounding enviroment. If you see a house take a shell, wouldn't you expect a fire? And not even that big of a blaze, maybe just like little areas of the building that are either destory-able or have a animaation of a fire with smoke that starts when they're hit by certain weapons. It wouldn't have to be every building either, just a few that can erupt into large infernos would be enough I think to give you the feeling that this area is devestated.
Something similar might be done to certain places on roads or in the dirt, where in the map they're can be 'shell wholes', but covered up by a destroyable 'piece' of dirt over it. So if a shell lands there it blows away teh dirt and you have some cover.

Now I also had another idea to make fire 'spreadable' in some instances. I'll use a room inside a house for example. Certain objects in that house might be similar to teh what I described above, when they take adequate damage, they have a flame animation. Now when the objects do burst into flame, they'd also have a small area damage effect. If you get close to it, you'll start to lose health. But the thing is, these objects can damage each other. So lets say theres a two story house. The building is pummeled by a bunch of shelling from outside. This sets the couch on fire. As the couch burns it does damage to the rug beneath it. The rug then catches and it spreads along the rest of the floor, which damages and lights the curtains, which burns a support beam, which when destroyed, crashes to teh floor beneath, perhaps killing anyone there. And I'm not saying FS should turn into a fire fighting mod, but I suppose it would also be possible to have fire extinguishers that can repair these objects, increasing they're health till they're out of the range where the object is supposed to be on fire, putting it out.
You know what, now that I think of it, how awsome would this be on capitalships? A Victory Star Destroyer starts to take some serious fire from a moncal cruiser. Their might be destructable object onthe surface of the ship (like we've talked about before, for destroyable ship pieces) that when destroyed starts a fire in exactly the same way as described above in the ship's engine room (or star wars equivilant). The fire will continiously damage the ship unless it is put out. Perhaps if there are certain places engineers need to go to repair teh ship, these places might also be blocked by fires.

Futurama: You Can't Prove it Won't Happen