While vacant lots have been filling in, I'm reminded of how much farther we have to go. Things look pretty different when the photo is more vertical, like the giant poster of
this by my desk, taken a month ago.
On one hand, the big parking collections are all reduced, including anything resembling a site where you could cram a stadium for example. But I'll make a wild guess: 100 parking lots in greater Downtown (out of maybe 2,000 acres), averaging 1/2 acre or 75 spaces. That would be 50 acres. If 40% of all land is street or park, that would be 50 out of 1,200 remaining acres. On second though maybe it's a lot more. Not counting street spaces.
Developable land is way more than that of course. We have a ton of buildings that made sense in 1920 or 1960 but don't today. Since the large vacant sites are mostly gone, larger projects tend to tear something down in addition to frequently taking parking lots.