As far as I understand the situation, it would be pointless to chase “unused” address ranges and try to claw them back because:
1. It would be technically very difficult, and old equipment is frequently hardcoded.
2. With the rate the allocations are going, you’d get maybe an additional few months or a couple of years out of this enormous effort. After that, all the addresses really would be allocated, and now what do you do?
Considering the huge effort, technical and political, it would take to do such a thing, it is easier to just adopt IPv6.
Yes this, we were blowing through a /8 every couple months in the past, haven't checked recently but might even be faster now. The parent argument comes up in every one of these threads.
1. It would be technically very difficult, and old equipment is frequently hardcoded.
2. With the rate the allocations are going, you’d get maybe an additional few months or a couple of years out of this enormous effort. After that, all the addresses really would be allocated, and now what do you do?
Considering the huge effort, technical and political, it would take to do such a thing, it is easier to just adopt IPv6.