I walk this area regularly. The loop using the Traveler's and W. 4th St. bridges is definite infrastructure porn.
My impression is that a reconstructed Dorchester Ave bridge to South Station should be first on the list of things to do.
As has been stated, access to the area is limited, and adding that connection would put Broadway at a 10 min walk from South Station. And it would do a lot other things too. Without getting bogged down in the numerous completing interests, this would be a concrete first step, and big one.