That's a great map to show to people who claim there's no way to "cram" more people onto the peninsula, which is a silly argument I've heard a number of times.
As far as adding areas, Quinpool Court/Quingate Place takes up a vast amount of room for a really ugly cluster of apartment buildings that could be redeveloped to a much higher density.
Alderney Landing and its adjacent block-sized parking lot aren't performing to a particularly high urban standard.
Other than that, it might require zooming into a more micro level. I'd suggest that the bit of the South End identified west of Barrington is one I wouldn't want to see change enormously. It's already among the highest density areas in the province, and contains some of the best historical residential architecture. Ditto bits of the North End identified outside of the main avenues. (Most of those streets seem to be increasingly full of homeowner occupied houses, with any given street being home to a dozen or more property owners, making it unlikely any big developments will happen anyway. I imagine that, say, Woodill and Moran and streets like that will look basically the same in 50 years as they do today, except the houses will be much more expensive.)
But while I certainly wouldn't want to see us start knocking down
this sort of thing just for density's sake, the 1960s certainly saw a lot of
stuff like this that's crying out for a swift death.
(I wonder if there's any way to direct development to the latter rather than the former sites.)