This theory is assuming that the game doesn't take place in 2277, but a little bit later.

Fallout 3 was a set up for Fallout 4. In it, we are introduced to Lyon's BoS Chapter, shatter the Enclave, and are introduced to Two factions from the Institute, the Railroad and the Scientists at the Institute itself. maybe the reason we don't visit the Commonwealth as the LW is because it's not his tale to tell. Visiting the Pitt makes sense as it can be seen as a resource for making new items for DC. Operation Anchorage shows the Outcasts having internal strife, and Broken Steel shows that on top of scattering the Enclave Remnants, the CWBoS is gaining strength and is now starting to help the major settlements of the CW. Not much to tell from Point Lookout other than there are boats capable of making the trek to the Commonwealth

Fallout 4 is based in Boston, and it's centerpiece is the Commonwealth set that we've been given. We play as a different character who has a different tale to tell, and (hopefully) we'll learn the repercussions of the Lone Wanderer. It's a place that we've only gotten hints at what struggles are happening, the sudden appearance of a more militarized BoS probably means a new Leader, probably taking the loot from Adams Air base and is now ready to expand.

The theory is that is is the Story Bethesda has wanted to tell with the Franchise. Whatever is going on in Todd's mind, we're about to see it.

I haven't been focusing too much on the plot of this game but I hope you're right and it does have plenty of continuity with Fallout 3.

Some nice background lore about FO3 would be nice, maybe we will run into Sarah Lyons, seeing as she is the natural person to succeed Elder Lyons should he no longer be in charge. But i honestly doubt we will realy see FO3 characters back, as manny have branching stories. Sarah Lyons could be dead, having sacrificed herself for activating the purifier, (that is if i think you dont take the DLC in acount) Moira could be either fine or a ghoul, megaton could be bombed or fine, etc. I do hope Bethesda hasnt decided to jam a canon story down our throats as people would be disapointed if their previous FO3 game playthrough is not what the world is based on. It would mean alot of RP'ing is not posible conserning set events in FO3 canon that contradict it.

But enought of my ramblings, i am looking forward to finding more out about the main plot of the game though.

Many events of F1 and F2 are canon too. And we already know that the Lone Wanderer helped Moira to make the Survival Guide. It don't destroy your roleplayability. You still can roleplay F1 and F2 however you like. And you still could play FO3 however you like. And I'm sure Broken Steel is canon.

DC to Boston is nearly 450 miles away, if they are there then they have certainly been expanding and rather rapidly. Some other minor places that they likely went through on their way to Boston are Philadelphia and New York City.

I hope Bethesda goes a different route than the Elder Scrolls for what is canon. It is nice to have the options during the game, but by the time the sequel comes out every possible way to play the game should not be canon. Since they are using Lyon's Brotherhood I suspect that we will see quite a bit of information about the events in Fallout 3, and I expect to see some recurring characters like Three Dog.

Wonderwombat: 'and I expect to see some recurring characters like Three Dog.'

I liked his record collection but if he does reappear I'll just have to track him down and blow his skull apart like I did in the last game.

Well, according too the leak documents from a year ago, the BoS is not the same as the Capital Wasteland BoS.

True, but we have no knowledge of how Philly has handled itself. All the knowledge we have been given about outside the DC wasteland is about the Commonwealth. Maybe it's that because of the Institute, the Boston area is a bit more secure as of 2277. That, or they have a lock on Ocean-fairing vessels and can make the trips. Whatever the reason, Bethesda has made this particular area very significant through in-game lore in Fo3, and I want to see how it all plays out.

Philly is described as "that dump" in a computer terminal in Rivet City.

The Liberty Bell is supposedly still there, and Abraham Washington plan to send a group to retrieve it.

Pretty sure it is supposed to be full of radiation, slavery, and raiding. So probably similar to the Pitt. I'm sure the BoS, some years after 2277, could pacify it if they wanted. Perhaps the initial BoS in Boston will be more of an expeditionary force, and it won't be until the end that they really arrive in force as they have been dealing with other land conquering.

The other option is the Brotherhood aren't after any expansionist goals, and you targeting them is the result of taking jobs from the Institute, that aren't really keen on having a bunch of "Neo-Barb" Tech Scavengers poking around their backyard.

Don't recall hearing that anywhere.

Looks like I remembered it from here. http://fallout.gamepedia.com/Eastern_Commonwealth