Re: "Therefore, assuming the powers-that-be would be willing to do so, in a super-high-tech regime several billion unproductive people could be supported in one or more tolerably dense enclaves at a relatively low opportunity cost. The real questions are whether the will to do so will exist, what troubles might ensue during the transition, and whether these unproductive billions will be able to form a tolerably functional society."
Organic humans becoming functionally redundant is likely to be the beginning of the end for them. They may well be able to persist for a while as useless parasites on an engineered society - but any ultimate hope for becoming something other than entities of historical interest would appear to lie with integration into that society - and that would take a considerable amount of "adjustment".
The question that the ideas are supposed to be in response to is:
Here are links to some proposed ideas that you should vote for, assuming you agree with them. You do have to register to vote, but the email confirmation arrives right away and it shouldn't take much more than two minutes of your time altogether. Why should you do this? The top voted ideas from this request for ideas will be seen by some of the top policy recommendation makers in the USA. They probably won't do anything like immediately convene a presidential panel on AGI, but we are letting them know that these things are really important.
Research the primary cause of degenerative diseases: aging / biological senescence
Explore proposals for sustaining the economy despite ubiquitous automation
Establish a Permanent Panel or Program to Address Global Catastrophic Risks, Including AGI
Does anyone have any other ideas? Feel free to submit them directly to ideascale, but it may be a better idea to first post them in the comments of this post for discussion.