What if Boston had become an island city?

Eric Papetti takes a trip out to the Harbor islands and wonders what if, instead of being turned into a park, the islands had become far more developed than they ever were:

... [C]onceptually, it's interesting to imagine Boston as being an "Island City," with a heritage that overlaps with others like Singapore, Hong Kong, Macau, and New York City. Would we build the city any differently if we conceptualized it like this? I'm always struck by how, in downtown Boston, the sea is something felt in a secondary way rather than seen directly. Even when one can't see the water directly, one is still aware of the smell of salt air, the occasional seagull, the quality of the light, and the presence of old maritime buildings. But when seen from the harbor, the city's true situation is easy to see.

Earlier:
What if they'd built an island in the Charles between Beacon Hill and Cambridge?