What incentive to a holder of early allocations is there to return address space voluntarily?
Zero. In fact there is a disincentive since it costs money to return address space. Most of these organizations will not have central control and management of IPv4 addresses with an automated system that can clearly and confidently report what addresses are not needed. Only ISPs implement systems like this and not all of them do so. Most organizations have pieced together spreadsheets, scripts, network discovery tools and departmental IP address management systems to do the job. The effort required to just get a clear and trustable report of which addresses are surplus will cost a considerable amount of money. This all comes at a time when the same resources (cash and people's time) should be working on planning how and where to deploy IPv6 within the organization for the greatest benefit and least disruption. The potential losses risked by a company for not being able to deploy IPv6 when and where they need it, are far greater than the potential benefits of selling a few IP address blocks. Even if you are talking about figures of $500,000 dollars for a /16 block, you still have to deduct the cost of figuring out that this /16 can be released without harming the organization's network. There might not be much profit left. This whole issue (IPv4 depletion) is likely to be written up in one or more B-school cases because this is classic MBA territory. There are no right answers. There is no solution to the problem. There are only courses of action which carry less risk and lead to more profitable outcomes. In my opinion, none of those courses of action includes participation in an IPv4 address market.
Efforts to redefine class E have stalled because there is simply no way it can be used for anything other than private space. There are too many implementations out there that will never be modified (e.g., Windows 98) on which you can't even configure class E space.
Class E could have been used if we had started a year ago. But now it is simply to late to do anything about it. The window of opportunity has passed. I'd still support moving Class E space to being ordinary unicast IPv4 space because it makes no sense to keep it special, but I don't believe that anyone will be able to use these addresses until well after we are into the mixed IPv6/IPv4 Internet phase.
IANA recently reclaimed 14/8. I think that added 3 _weeks_ to the expected runout date. That was likely the last "easily" reclaimable block.
Easily!? I'm not so sure that is a correct description of the process. Perhaps Leo Vegoda could comment on this point since he had more first hand involvement than I did. --Michael Dillon