When the Volpe building is removed, extend (actually re-extend!) the canal west to terminate at the existing lawn on the western portion of the Volpe site. The lawn and it's mature trees should be preserved and serve as a book-end to the canal, a public gathering space for the Kendall Sq area. The canal would be bound by a canal walk on both sides as well as parcels for development.
Completely redevelop the Fresh Pond Shopping Mall site creating a linear pedestrian mall lined with retail, parking on the back sides, preferably in structures. To the south linear corridor would connect to the recently acquired Watertown Branch RR (to become a trail), and a new pedestrian/bike bridge over the tracks connecting directly to Alewife Station to the north.
Fine example is in Downtown Denver with a new pedestrian corridor extending NW from Union Station pedestrian corridor with multiple bridges and new parks.