Even with a pessimistic estimate about the rate of progress, fully general AI will be here loooong before population decline decimates the economy, as will good robotics and all the stuff needed to basically put resource gathering and production on autopilot. At that point "on welfare" would easily be the equivalent of living like a millionaire today.
The bigger questions are whether global warming or WW3 will fuck us all before we get there, not to mention the question of whether fully general AI will be its own mega disaster.
Population decline will be a problem in your lifetime. I’ve become disillusioned with the idea that hyper-automation is just around the corner. Observing a Chrysler assembly plant from almost a century ago, vs our current car assembly plants (wiring harnesses still very stubbornly manual), has tempered my expectations of automation progress, as has the slowing of Moore’s Law and the failure of self-driving-cars to materialize in the last few years.
Seeing modern day "best in class" is a great way to become pessimistic about progress, you see the best of now but don't realize it's the worst of "soon". In 8 years you'll reverse course completely based on machining automation, and in 11 we'll have true AGI.
The bigger questions are whether global warming or WW3 will fuck us all before we get there, not to mention the question of whether fully general AI will be its own mega disaster.