Some of Bioware's games function entirely on working as a party and switching between characters. Some of the mods I've seen try to emulate this.
I forget which one it was, but there was a mod that allowed the player to set certain companions as team-leaders, and they would in-turn lead a group of followers. If commands were given to any of the leaders, they and their companions would carry out the order. They also had several functions that let them travel to specific inns and such, which I think was a great social addition to the game. "Hey, you guys go hang out in town a while, we'll catch up later."
Another thing that's rather bothersome is that NPCs barely have any concept of where other companions or the player are facing, so it's easy for them to walk in the way of spells or attacks. Likewise, in reality if a person is trying to touch a person (casting a spell) it's much easier to keep track of where the person is going, thus easier to touch them if they move. In the game, if someone moves out of the way of a restorative spell (or destructive for that matter), it's hard to track them.
Sometimes, companions are just kind of stupid.
Here's an interesting afterthought I just had; design dungeons and AI to where an NPC has the capability to dungeon-delve if he decides or if the player tells him to. If he feels used or neglected, he could steal some of the treasure for himself.
Do you think the Elder Scrolls series could benefit from such an integrated party system, either as DLC or in future games? What aspects do you think would be most beneficial?
Would switching between party members break immersion? Perhaps it would be like fast-travel; use it if you want, but roleplayers choose not to?
Or does the whole idea just not feel very Elder-Scrolls?
Edit: In this, I mean optional additions, rather than changes to the base formula. Though, if you like the idea of full changes, feel free to support them.