Thanks for writing!
One trend in longevity-enhanced cultures which I expect to become common, is for “old and worn-out souls” to trigger a kind of mental rejuvenation: Use some type of medicine/gene-activation/.. to trigger a softer version of what happens during childhood.
I see several reasons:
This would allow for a culturally-acceptable and powerful method for people to reinvent themselves and start anew (possibly with an agreement that the usual date is every 100th birthday), which would be a more important element to cultures suitable to longer life-spans.
Also (depending on how the immortality works), I would assume that people would wish to have the ability to reinvigorate their “passions of the past”. I think it is quite common that older people lose many of their interests and replace them with “their legacy” and “watching the young ones”. If this isn’t directly inhibited by the life-extension, a method to reduce or revert this change would become important.
I don’t know enough about this to be sure, but I’d be surprised if our brains operate in a way that does not in some sense accumulate brittleness (weak enough that it typically isn’t important for current(/past?) lifespans). Finding a way to stabilise this would be important and “just hit restart” seems like a plausibly helpful and achievable approach.
I think that this would change the dynamics described in the OP quite a bit, as the cultural dynamics (exploration) could stay quite strong. Also, this might weaken the forces that create a gap between longevity-enhanced and normal-longevity people.
I notice that human DNA has 46 shards. This looks to me like evidence against the orthogonality thesis and for human values being much easier to reach than I expected.