Probably silly to even talk about but it occurred to me as I read those books that in reality a “Generations Ship” captain will feel pretty silly when he arrives at his destination to be greeted by his great, great, great,...great, grandson who arrived thousands of years ago shortly after the “Generation Ship” left thanks to new technology.
I think this is where we are with humanities “next step”. No one wants to be the guy that sent those generations into space needlessly. So the “ONe step for Mankind” was important and what we are undertaking now is important but the real goal is faster than light. That is the barrier that has to be broken and I read just the other day that the mathematicians say it is possible. Something about accelerating the reality around the ship so “locally” it is not breaking the light barrier.
So the gravitational drive in the book may actually be a possibility. Which is what I loved about the books. The author really does a great job of incorporating the latest knowledge.
If I recall in the 3 body series the use of the FTL drives were like a beacon to anyone paying attention, and everyone powerful enough paid attention just so they could destroy other civilizations as quickly and inexpensively as possible. Pretty grim stuff, one plausible theoretical explanation why we seem to be alone so far.
Freegards
All a "generation ship" is is a space habitat with a drive system. Space habitats will be among the very first fruits of man in space.
Once the tech has developed sufficiently to be "semi-closed", I suspect that some humans will say "who needs planets". Once "habitat civilization" reaches the Oort cloud, it is pretty much a given that some will take the jump to the Oort cloud of the nearest star system.