I cant believe that no one has mentioned they city that has the most history and importance when it comes to the US. Philadelphia. It would be interesting to see Fallout 4 take place there. Its not too far from the Pitt or the Capital Wasteland, so it would probably be affected by the events in those 2 areas.
And instead of a Vault Dweller, I think the character should start off as part of a raider group. So far, the other Fallouts have done characters from vaults, the BoS, from tribes. I say its time for Fallout to dive deep into the world of Raiders. The player starts off as a raider. You pal around with your radier buddies, pillaging a few villages, murdering a few dozen people, and leaving a trail of chaos and destruction in your wake. Then, one day, your gang gets wiped out by a group of mysterious strangers and youre the sole survivor. Left alone and barely alive, your found by some travelers who take you in and nurse you back to health. But now, your character is on a quest for revenge. You're going to find those people who killed your gang and make them pay. However, because of the kindness shown to you by those nomads who found you, your character has seen there is good in people. A moral dillema arises. Do you continue on your raider ways, killing and pillaging people like the ones who helped you? Do you turn over a new leaf and pursue a life of virtue in a land bereft of any sort of morality? Or do you walk the thin grey line of neutrality, mixing your actions with deeds both good and evil?
And the child killing thing, they should definitly have that in. I wish it had been in Fallout 3. Those brats at little lamp light got on every nerve I had, especially McGreedy. I hate that little jerk..... so very much. What I wouldnt have given to have been able to introduce him to the barrel of a missle launcher... MUNGO THIS YOU LITTLE CREEP!
You see, this is exactly the kind of 'moral ambiguity' we are looking for. Somebody up high should pay attention to posts like these, they contain interesting suggestions.
It would be completely new to the Fallout franchise if you could actually join the bad guys (Fallout 1 let you do it but it conclusively ended your game), or just BE the bad guy. I loved what they did with Jedi Knight: Dark Forces II where you could actually use the force to stop your arch-nemesis from becoming omnipotent, or using it to destroy him and then take his place as the evil bastard all powerful ruler of the galaxy.
Also, yes kids should be killable. In Fallout 1-2, I don't think any of the kids annoyed you to the point of you wanting to kill you (except maybe the robbers at the den), but its ridiculous when you make them extremely annoying, and immortal.