I'm sure storylines are already covered in the immense amount of topics created in this forum. Even so I'd like to put in my 2 cents towards what the game is going to aim for.

Are we going to just wander around killing things and just surviving in this game or is there going to be a main storyline that is concurrent with the lore of the Fallout universe.
I believe if there is a main storyline it should be the rebuilding of America or where ever it is set. I don't care how long it takes to reach the end. I just want a main storyline that, in the major scheme of things, will eventually end up somewhere.
Finally build up and work towards a goal of the restoration of the post apocalyptic world.
Of course we could then have a side to choose. Those who go against it and keep with the anarchy already dominating the Fallout universe or the side who wish the old world to be restored.

Fallout games have a way of having story trees rather than story lines, but Each branch has each their storyline. some which ties up in the end

My dream come true would be that main events would be caused by the state of the different storylines, specific example the ratios between the levels of player compounds. one side having the advantage= one line, the other side having the advantage the other line, both within a certain level= a third line.

the measurement that triggers the response could be anything.