I think you agree here as the situation you describe as a likely outcome is by no means desirable ... an elite group of humans enforcing the complete subjugation of the rest of the planet.
It's not subjugation if all they do is prevent independent outbreaks of destructive technology.
I can see that I described four forms of posthuman technocracy, that we could call wilderness, meritocracy, exploiter, and cult. (Don't hesitate to employ better names if you think of them.) Wilderness and meritocracy are the ones that you quoted and I can't view them as bad, in fact they could be positively utopian. We're talking about a world which has solved the crisis created by technology, by arriving at a social and cultural form that can employ technology's enormous potential constructively.
Such a world has to ensure that the crisis isn't recreated by independent reinvention, and it has to regulate its own access to techno-power. The "policing" is for the first part, and "entry exams for the techno-aristocracy" is for the second part. Do you find the prospect of even that much structure depressing, or is it just that you think the dystopian possibilities would inevitably come true?
You also dismiss the problem of over population, lack of resources, and colonisation of space ... Instead of looking for contingency plans we should confront the problems of global warming lack of food and energy sources directly.
We should distinguish between any exacerbation of existing problems due to longevity (your first list), and the problems that already exist and would continue to exist even without extra longevity (your second list). Just so we have names for things, I'll call the second type of problem a "sustainability problem"; a technological solution to a sustainability problem, a "sustainability technology"; the first type of problem, an "exacerbation problem"; and a technology implicated in an exacerbation problem, a "destabilizing technology". So we can call, for example, solar cells a sustainability technology, and stem cells a destabilizing technology. (These are precisely the sort of ultra-broad categories that can lead you astray, because under certain circumstances, solar cells might be destabilizing and stem cells might be sustainability-enhancing. But I felt the need for some extra vocabulary.)
So I summarize this part of your position as follows: we should prioritize the solution of sustainability problems, and avoid exacerbation problems by staying away from destabilizing technologies.
There's a large number of sub-issues we could explore here, but I see the central fact as the failure of relinquishment as anything more than a local tactic that buys time. Someone somewhere will develop the destabilizing technologies. Independent development can't be prevented or "policed" except by someone already possessing similar powers. So ultimately, someone somewhere must learn how to live with personally having access to destabilizing technologies, even if these powers are locked away most of the time and only brought out in a crisis. The various "posthuman technocracies" that I sketched are speculations about social forms that don't keep advanced technology completely sealed away, but which nonetheless have some sort of resilience.
I don't think we should allow our selfishness to corrupt the natural continuation of the human race.
Well, the moral and existential dimension of these discussions is hotly contested. I focused on politics and pragmatism above, but I'll try to return to the other topics in the next round.
You didn't say destructive technologies you said "technologies of power" implying that the technological and scientific domains in this hypothetical future world would be stifled or non existent in order to prevent humans grasping power for themselves and threatening the reign of this "post human technocracy". This sounds like subjugation to me. You also say they would "decide what would become of the rest of us". This also sounds like complete totalitarian domination of the "old style human beings". Considering that...
If you don't believe in an afterlife, then it seems you currently have two choices: cryonics or permanent death. Now, I don't believe that cryonics is pseudoscience, but it's still pretty poor odds (Robin Hanson uses an estimate of 5% here). Unfortunately, the alternative offers a chance of zero. I see five main concerns with current cryonic technology:
So I wonder if we can do better.
I recall reading of juvenile forms of amphibians in desert environments that could survive for decades of drought in a dormant form, reviving when water returned. One specimen had sat on a shelf in a research office for over a century (in Arizona, if I recall correctly) and was successfully revived. Note: no particular efforts were made to maintain this specimen: the dry local climate was sufficient. It was suggested at the time that this could make an alternative method of preserving organs. Now the advantages of this approach (which I refer to flippantly as "dryonics") is:
There is one big disadvantage of this approach, of course: no one knows how to do it (it's not entirely clear how the juvenile amphibians do it) or even if it would be possible in larger, more complex organisms. And, so far as I know, no one is working on it. But it would seem to offer a much better prospect than our current options, so I would suggest it worth investigating.
I am not a biologist, and I'm not sure where one would start developing such a technology. I frankly admit that I am sharing this in the hope that someone who does have an idea will run with it. If anyone knows of any work on these lines, or has an idea how to proceed, please send a comment or email. Or even if you have another alternative. Because right now, I don't consider our prospects good.
[Note: I am going on memory in this post; I really wish I could provide references, but there does not seem much activity along these lines that I can find. I'm not even sure what to call it: mummification? Probably too scary. Dehydration? Anyway feel free to add suggestions or link references.]