>>4
The end of scarcity I think only implies that resources are so abundant that they can easily supply not only needs, but also the ever-growing wants. It doesn't imply anything about unlimited supply or anything at all about equal distribution. Distribution is a service problem which either will be handled automatically by robotics or by people in the service industry. People will still want to work and earn credit/money that can be used either for fame or for the limited resources that must exist in any society, such as time at desired locations (resorts, ocean front properties). If we go full science fiction we could foresee full body immersion as well as a way for people to forego those limitations of experiences as well.
Elites might remain in power, but in power of what? If anyone in society can easily produce or obtain goods and services without any difficulty then there is no means to control. Consider for example just a few techs: 90% efficiency solar panels with advanced 3D printers with near replicator (StarTrek) like efficiency. Maybe such tech is impossible or forever beyond limited human understanding, but the combination of those two would leave very limited needs to be fulfilled, such as housing. I think pessimism is only natural with daily view of the corruption and greed in today's elites, but it is hard to know if that will always be the case.
1.What makes you think it wouldn't be some elite class exclusive to be a cyborg and millions will never afford it?
This is very likely. But for how long? Will the first people that become advanced cyborgs forever wish to keep everyone as replaceable cattle? Will their live-spans be extended? and if so will they want to be forever alone as others die? It is possible, but we cannot assume their mind will not also be enhanced, and become something more than human. We cannot be sure how that will affect them, or what their motivations will be. There will likely be incentives for this tech to become available and reasonably priced, otherwise the companies that invested money on research and development of such products would lose money.
2.If the cyborgization will be cheap and widely available, what prevents stratification, like millions of "worker drone" humans vs super-cyborg elite who have best augmentation?
What prevents this? Not sure it would be prevented. But don't forget about CRISPR and brain enhancing tech. Would you want worker drones that are prone to injury or robotics however? At some point and in some fields those worker drones are likely going to be more costly than robots. We can already see a trend towards automation, but it is difficult to predict the future.
3.If genetics is the pathway, what happens to billions who can't afford it? Genetic modifications have to be tailor made to genotypes.
I have no idea if "billions can't afford it" is the forever truth or just the temporary truth. There will also be many that (even if they can afford it) will choose to not, for fear or religious reasons), but it is difficult to know if they will hold out for generations or simply years. In time I suspect it would take an incredibly strong cultural indoctrination or imposed ignorance upon their children to keep their children from seeking out potential real life immortality (assuming that is possible). That would also require those living beyond scarcity to feel near zero empathy for those living in relative squalor. The unempathetic mind that humans have today might be a result of factors that wouldn't impact 100% of the people living beyond scarcitc, so they may wish to bring them into "modern" times and improve their living condition. Of course that might mean bringing them under a surveillance state, as seen in popular novels.
The link between the singularity, end of humanity as we know it, utopias, and dystopia is hard to predict.
Human slave labor has been a highly profitable system to exploit, be it slavery or simply wage slavery. AI might take that system from the elites and rule over humanity, or maybe the elites will merge with AI and continue their rule. Maybe humans will persist under such a system for some time, but I don't think it will be hundreds of years. I highly doubt human slave labor is the pinnacle of efficiency, and over time incentives will drive robotics to replace meat things that need and inefficient amount of rest and sustenance.