Thanks a lot for pointing out some issues with my approach.
I am quite aware, that I should have extended this post and included more quality of life aspects.
At least in the German adaptation of that post I included an update to clarify some of the problems with the used data and missing information. I will maybe write a follow-up post about this topic in the future in order to address some of these issues, many people pointed out.

True, but, again, let's be practical: you think the rich are just going to equally distribute all their wealth? I don't see that happening now, so I've no reason to think it will happen in the future. Death and war are more likely, I think.

Personally, I don't think that is going to happen. Judging by the data regarding the number of violent conflicts and relative death tolls, we are still living in an incredibly peaceful time. I don't think, wealth needs to be redistributed, but with more and more ways to produce cheaper goods, the overall quality of life will increase. This is something, which already seems to happen in many countries.

There's no way (according to economists) the young population can sustain the increasingly older population.

Again, this is most likely true. But this is not so much an issue of demographic change but a flaw of the way societies take care of their older population. In Germany, for example, this is mainly done by laws and taxation - which, of course cannot work out, since the mere numbers don't add up anymore. I think people need to be more aware, that there best shot is to invest their own money wisely, so they have something to live on as they grow older. The state policies are only going to fuck things up.

and the natural follow-up to that is the transhumanistic movement, but I don't think the reader who doesn't already know about this stuff appreciates how that relates to the rest of your argument in the post.

Yeah, you are right. And, in fact, you just gave me a reason to write a series about transhumanism as well. Thanks a lot for increasing my (quite long) bucket list :D