Everyone knows IPv4 addresses are scarce these days, but what's really happening in the IPv4 address space?

An analysis of the server logs of one of the largest CDNs indicates that starting in 2014 the unique number of active IPv4 client addresses leveled off, ending a period of predictable growth. However, the majority of already-assigned blocks seem to be grossly underutilized; for example, more than 1.5 million /24 blocks were observed actively using just 25% (or less) of their available addresses.  This suggests one path to relief for IPv4 address space shortage: network restructuring. While restructuring can be resource and time intensive there is enormous potential for recovering assigned but unused space.