It seems to me that adding something like this would be rather pointless, since the main focus of the series is on questing and exploring, and I expect this will remain so in Skyrim. If a feature like this were in the game, it would probably just be done in a half hearted manner, which would just make it boring and a waste of the resources it took to implement it. I think I agree with greatcarbuncle here, things like this need to be the main focus of a game for it to be done well.
I could see a few instances of large battles during quests, of course, but these would probably have to be scripted events. Allowing players to actually declare war on anyone they please at any time just sounds like something best left to Civilization to me.
That Battle for Bruma sure was disappointing.
That's because Bethesda tried to make some large, epic battle but the engine simply couldn't pull it off. Hopefully, though, Bethesda has learned from that mistake. If Bethesda is going to try to do battles like what the Battle of Bruma was MEANT to be, then hopefully, they'll have an engine that can do it properly. Otherwise, they just shouldn't try, not every story needs to have battles involving thousands of combatents on either side, sometimes, it's okay to just have the player facing single or small groups of enemies too, as the engines in Oblivion and Morrowind, at least, seem to handle that much better.
Plus I had leveled far enough that the enemies were all infinitely more powerful than my allies who were for some reason the ONLY ****ING THING in the game that didn't level with me.
I've noticed that problem with a lot of quests where you have allies, actually, Breaking the Siege of Kvatch was also one that suffered from it. Generally when I did that quest, it would not be long before Savlian Matius, or however his name is spelled, was the only guard left alive, and only because he was essential. Hopefully if we get quests where allies try to "help" you in Skyrim, they're actually helpful, as opposed to getting killed by the first group of enemies you fight during the quest. Otherwise, I'd honestly rather it be like Morrowind where you spend a long time traveling across Vvardenfell to get people to support you as the Nerevarine, and then when you need to raid Red Mountain, no one comes to your aid anyway.