First of all, I would like to start out by giving a big thank you to everyone who has worked so hard on this game as well as those who are still working on it. I'm currently in college studying 3d CG/animation and I have a whole new appreciation for projects like this.
It seems that the wonderful system shown at E3 in which you can build your own settlements will give players another reason to continue to play the game after beating the main story line. It might be really neat if you could somehow interact with other players settlements. This idea seems to find its way drifting toward an MMO feel, Fallout has never been an MMO, that is where the real challenge lies. I hit a wall when I try and think of a way to make fallout an experience that can be enjoyed alone, but also enjoyed with friends. The only way I can see both happening is by taking the plunge into a co-op or multiplayer experience.
If anything, it would be interesting to see a mod in which a player could join a private lobby and help you build and defend your own wasteland! I think making such an option a standalone game mode would be the only practical way of implementing it in a way that wouldn't mess with the single player experience.
I'm sure the team at Bethesda has a few more tricks up their sleeve they won't be revealing right away. I know the game will be rock solid.
Any fresh ideas on how this game could be enjoyed with friends would be much appreciated, as well as any feedback.