I appreciate your willingness to actual consider this rationally.
Every facet of this debate has been fully aired on this forum (and others), numerous times.
Allow me to pick it apart again. Apologies to those who are ad nausem.
Eric Kuhnke wrote:
Option A) Spend engineering time and equipment purchases to implement 240/4 as unicast globally. At present consumption rates and based on the number of entities in ARIN, RIPE, APNIC regions that could *immediately* take /18 to /16 sized blocks of it, please quantify exactly how many years this amount of "new" IP space you predict to be useful before once again reaching ipv4 exhaustion. End result: Problem not solved. Thus my analogy of building a sand castle while the tide is coming in.
Option B) Spend engineering time and equipment purchases (yes, very possibly much more time and more costly) to implement ipv6.
This is know a false dichotomy. There is no actual reason to believe that any effort on option A detracts from available effort of option B. And when you purchase your new gear, or update the software, with its many many lines of code changes, it is not unreasonable to expect that at least some might be IPv4 related and that the removal of restriction on 240/4 would be the more trivial of those.
Indeed that is exactly what has been happening since the initial proposals regarding 240/4. To the extent that it is now largely supported or available across a wide variety of gear, much of it not even modern in any way.
Further, presentment of options in this fashion presumes that we have some ability to control or decide how engineering efforts across the entirety of the internet should be spent.
Respectively, amusing and alarming.
To be clear, the only thing preventing the Internet in freely organizing its own efforts is the unwillingness of curmudgeons to remove the reserved status in this particular instance.
As no-one is requesting that you (or others of this persuasion) lend their personal efforts, your concern on the budgeting of efforts is out of place and worse, of dictatorial bend.
For the sake of argument, ignoring above, presuming our control over the internet engineering efforts et al.
Were I to propose to you that 240/4 be utilized only for new or existing organizations with less than /20 total resources or some other useful constraint, it would be easy to see that 240/4 would last a very long time and potentially have quite a significant impact.
Earlier in this thread I contrasted a reduction from 12 to 1 of ip address consumption per new customer, depending on the practices employed by the service provider. As you can see, consumption rate is actually quite flexible, even now, today.
So the answer to your question is it depends how freely it is handed out. Certainly not very long if it is business as usual prior to runout. Potentially much longer if not.
And in a nod to your concern over effort expenditure, but even more so, conscious of 240/4 being the 32bit space last big easy gasp, I would be a strong proponent that it NOT be.
However, even if it were, what exactly are we saving it for, if not for use by those who need it?
Or is it to be a hedge over some eventuality where IPv6 has failed to the point of abandonment? I might actually respect that position, even as I doubt (and fear and hope against) such an eventualities actual occurrence.
The more galling aspect of the 240/4 wars is that "it will take too long and then Ipv6 will be deployed" crowd that managed to stifle it initially continue to reuse that line again, in essence blase self perpetuation.
Its only taking that long because of this attitude.