i think there are a lot of aspects of it you can anticipate even if it is incredibly alien, you might not be right about everything but you will probably be right about some things.

its quite possible to speculate about cultural changes that might arise from near lightspeed communication, thinking at 5 gigahertz, brain encryption, software brain cloning, software brain merging even though those are all alien scenarios to our current daily lives, you can draw boundaries around the space of possibilities and you might be right about them.

i have no idea what comes after a dyson swarm but I doubt it will be finished (assuming no ai ruin, which you can also speculate about) sooner than a hundred and fifty years, maybe even 500 years from now which is pretty far out.