I'd love to see more chances to build up central/urban areas in the DLC. The houses around Bunker Hill, for example, are pretty much in-tact. Why just keep people in shacks? Wouldn't the SS try to build an administrative center? Supply lines could provide an exchange of goods (ie. crops) in exchange for protection and/or rare resources, a la the Roman Empire. Perhaps this option could unlock after a certain number of settlements have been established?

Also, some people (including me) have requested a better management system for resource allocation. Most of the settlers are unnamed, so I forget who I've assigned to what resource. Perhaps this management could be conducted through a terminal at some centralized location, if not the player's Pip Boy.

From a gameplay standpoint I think large municipalities are just beyond the scope of the game. The SS should be mostly out hunting and killing, not running zoning board meetings.

From an internal logic standpoint I think that the absence of such large settlements implies that, at this point in human history, they just aren't possible. A settlement gets to a certain size and it becomes an irresistible target for raiders, super mutants or god knows what else. The Minutemen are barely able to protect groups of 25-30 people. Even the BoS, probably the strongest faction in the game measured by brute force, only holds an airport.