Oddly enough, someone proposed something very much along these lines at a couple of RIR meetings (see "IPv4 Soft Landing"), and in fact used the 'driving into a brick wall' analogy. Many of the folks who commented on that policy proposal felt it was inappropriate for RIRs to dictate business models (that is, if an ISP doesn't want to move to IPv6, it wouldn't be 'right' for an RIR to force them to). The proposer eventually gave up as the impedance mismatch between reality and the RIR policy making process became too great to observe without breaking into uncontrollable giggles.
A more interesting experiment: We want uptake of IPv6, right? Allocating even fairly large swaths of IPv6 to those who didn't really need it would be less harmful than hoarding IPv4, right? How about actually providing an incentive to return IPv4 space? How about actually providing an incentive to provide IPv6 services along the way? For example, here, we're not currently doing production IPv6, because we're not likely to be able to justify the cost of acquiring space from ARIN. Our legacy IPv4 resources cost us nothing, both what we advertise and what we don't. If there was a way for us to trade in some swamp for IPv6, we might be tempted to do that, which would encourage IPv6 a little more. It would have to be on the same or similar terms as what we currently enjoy, otherwise, it makes more sense just to retain the IPv4. Further, there may be organizations that could be tempted into returning paid ARIN allocations, perhaps by offering them a guaranteed low rate (free, ideally) for IPv6 space in exchange for significant chunks of IPv4 returned. Now, really, would this be successful? Who knows. But I do know that it wouldn't be costly in any meaningful way. If the RIRs get any returned IPv4 space and hand out some free IPv6 space, "we" (the whole Internet) win on both fronts. Maybe the RIR isn't making oodles of money from registration services for that space, but then again, I've never been convinced that the pay-for-addresses model is a good idea in the greater picture. At some point, it would make sense to evaluate the question of how much IPv4 space is being sat on because of the costs of registering IPv6, etc. Of course, this is the opposite problem: we're now talking about dictating RIR business models. :-) ... JG -- Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net "We call it the 'one bite at the apple' rule. Give me one chance [and] then I won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN) With 24 million small businesses in the US alone, that's way too many apples.