But, I am not actually appealing to common sense here -- that would make me no better than the "no infinite growth in finite world" people. So, are you suggesting that people will no longer be able to be of any value to others at some point in the future? Or that, despite them being able to produce such value, there would be no demand for their time? Why?

I've seen that link btw. For some reason people in physics are particularly susceptible to thinking that they can understand economics better than economists do. They are quite wrong about that :)