Consider:
Boston is a port city. One can tell from the preview video that it's done a better job than most in keep itself at least partially functional. In other words, civilization of a sort still exists in Boston.
Now:
The Vikings sent traders and settlers to Greenland, Newfoundland and possibly as far south as the St. Lawrence waterway. If there are any european coastal cities that are in somewhat the same shape as boston or vegas, maybe they might get interested in sending sailing ships to other ports for trade purposes.
The trade could take various forms - agriculture, minerals, finished goods (especially weapons), maybe even technology.
Any idea if this will be evident in FO4? If it's not there now, how about including it in a DLC/Expansion? It might be incredibly fun to have a DLC based overseas.