Interesting, maybe we should revoke IPv4 assignations to Apple, Ford, HP, Prudential etc. who aren't using anything close to the 16 million IP addresses they have.
With the recent IPv4 address burn rate — the allocation rate the last remaining addresses block were issued — reclaiming a half-dozen /8 blocks would be a rearguard action at most, and an effort and a hassle that would detract from IPv6.
For data, select the column with the IANA date sort here:
http://en.wikipedia.org/wiki/List_of_assigned_/8_IPv4_addres...
and then consider how long a few more added /8 blocks would really last. By my count, fourteen /8 blocks since 2009. And the rate that network-connected devices are arriving isn't slowing.