Immigration only stays an option if you prevent other countries from developing.  

Immigration was a great solution for the US when when Latin America had above repopulation fertility rates but that is no longer the case. 

"homophobia ("cultures that accept gay people on average have lower birth rates and are ultimately outnumbered by neighboring homophobic cultures", in a piece that is all about how low birth rates are a key problem of our time)"

How on earth is the homophobia? A core concern of this piece is that there will be increase in the rate of homophobia as a result of this trend. Are you arguing with the trend, do you want statics? Here is a study that dives into this trend.

From 2004 to 2018, differential fertility (more conservative people having more kids) increased the number of U.S. adults opposed to same-sex marriage by 17%, from 46.9 million to 54.8 million.
Vogl, T. S., & Freese, J. (2020). Differential fertility makes society more conservative on family values. Proceedings of the National Academy of Sciences, 117(14), 7696-7701.

Also, how is this "ethnonationalism ("based in developed countries that will be badly hit by the results of these skewed demographics")" ethnonationalism? 

This point is brought up in the context of most of EA funding and activity happening in developed countries. It is just a fact that developed countries will be hit harder by demographic collapse.  Are you arguing the most EA funding does not come from developed countries or that developed countries are not disproportionately effected by demographic collapse? Or that both things are happening and we shouldn't care because more EA money will come from developing countries in the future? 

"I believe that genetics influence individual personality, but am very skeptical of claims of strong genetic determinism, especially on a societal level." That's not how genetics works.  At an individual level genetics will always be less predictive than it is at the population level (e.g., if I know a certain persons polygenic risk score my ability to predict how they will vote will intrinsically be lower than my ability to predict how a large population will vote if I know all their polygenic risk scores). 

Think of it like this. If I know an individual card has a 60% probability of having a blue dot on it that represents a vote for a specific political candidate  that is all I know.  However, if I know that is true for 100K cards then I can predict with near certainty what the overall "vote" will be. 
We are not genetic determinists at all (we even wrote an entire book on cultural determinism). However! We are also not science deniers. At the population level you can make predictions based on genetics and one of those predictions is voting patterns. 

Very thorough report, reminds of my thesis. Sadly, I wrote that thesis just as enthusiastically a decade and a half ago.  (I want to clarify this comment is only referring to the parts of this document that discuss central nervous system BCI being used outside of medical contexts.)

I started my career in central nervus system invasive and non-invasive BCI almost a decade and a half ago. I left the field to go into VC and PE when I realized how stuck it was.  I read this report excitedly to see if any new technology had broken through the core barriers that explain why the field has moved so slowly and my take away is that at least in those areas (central nervous system recreational BCI) we are at a complete stand still. Most of the tech you list as new in central nervous system BCI was around or at least being talked about regularly when I was in the field so while it is "new" in neuroscience terms it is nowhere close to AI timelines. 

Why is the central nervous system BCI so stuck? The non-invasive stuff can’t get around the stuff that surrounds our brain acting as a low pass filter, (ECOG solves for this but no one is going to get a BCI put under their scull for recreational use). As for the invasive stuff astrocytic scar formation is still the major block of long-term use (basically your brain starts to build scar tissue around the input device and the device needs to create "louder signals" to get through the scar tissue causing yet more scar tissue). This is solvable with (and has been for a while) with immunosuppressants but again that largely rules out recreational use (which was the only thing that interested me). 

Still, I am glad to see people still pushing ahead at the field. If everyone allowed themselves to become as dejected as I did it just because it moves so much slower than other EA relevant fields nothing would ever advance.  

What is your estimate on a timeline for a person of average income to afford said cure? What year do you estimate it would be available?  (I ask because while I agree with you even basic medical care is not available to most people in the world right now. I suppose it depends on the mechanism of action of the aging cure - a viral vector might be inexpensive to produce in mass.)

Note: Adding your suggestion to the document