The guys at Kokugamer have put together a brief list of features and other content that they'd like to see in Obsidian's upcoming Fallout: New Vegas. I doubt we'll see a co-op component, but I bet these two end up in the final product:
Returning Characters from Past Games
It's always a treat for the fans when they get the chance to see a familiar face. It's an even bigger treat in Fallout when it's both a familiar face, and one who isn't looking to take your head off and devour it. Due to the locale shifting coasts again for New Vegas, one would hope to see a classic character like Sheriff Marcus (voiced in Fallout 2 by Micheal Dorn), or even Goris. Though most players are probably expecting the return of the big bad known as the Enclave, and the New California Republic, one would hope that it wouldn't simply be old organizations returning, but also some folks with a gun that's aimed at someone else's head aside from your own. The unfortunate thing is that series mainstay Harold more than likely won't be in this next installment, due to him being very much rooted in the Capitol Wasteland, so to speak.
An evolved dialog system
Don't get me wrong. There was a lot of memorable dialog in the third game, and there's been plenty of it in games prior (with my favorite being with Harold in discussing power plant repairs in Fallout 2). However, it may be the right time for Fallout to possibly bring the (Talking Head) style of conversation up to speed, possibly by giving the player a voice of his or her own, and even allowing the camera to shift around the room, allowing for conversations to be a bit more dynamic in their approach, not to mention adding a bit of depth to the gameplay. For example, though the prologue of Fallout 3 was incredibly unique in how you literally are born and raised in the game world, players could have become a bit more attached to the character of James if the camera had shifted to a third person and showed him holding his son/daughter or somesuch. Usually when a character is voiced by the legendary Liam Neeson it's not necessary, but it still would have been a nice touch.