So i didn't see any hostile attitude or battles between two different cultured monsters or NPC's in Morrowind, but i did see some in Oblivion. If anyone did the Theifs guild quest to go and get the Elder scroll from the Imperial tower, you would know that while going through the passage a lot of rooms had goblins and zombies battling it out. I would like to see more of this in Skyrim. Why? Simply because it makes since, i mean in the real world, does everybody just attack YOU and not others as well?
Hostility in my opinion will make the Skyrim world more fun, exciting, and you might even get caught in an actual WAR. I mean imagine this :
You walk into a dreary cave. It has been said that goblins inhabit it. Although wierd noises have been heard coming the cave. You explore it. Out of no where you see goblins being pummeled by a pack of black bears. After the fight (or during the fight between the Goblins and bears) you hope in to slay the left overs.