To me the question boils down to one very simple point. If machines can do everything, then why would they need us? What's the basis for human existence, what's the basis for human skill or knowledge, for compensation? Do we get warehoused until some bright boy robot decides there's no reason?
Think about a war fought by drones, and the question is "why"? There's no personal stake, no personal risk, it's basic insanity. Who loses? The first team who runs out of toys? That's been a thought that I haven't been able to answer since the first articles published about AI drones on the battlefield and in the air. If there's no personal risk, then what's to prevent perpetual war? Why not just press the nuke button now and get it over with? If you think about AI as being logical and deciding there's no reason for war, then what if the particular brand of AI evolves into one that believes in conquest/domination?
Imagine a tennis match played by robots ... why ... de dunk de dunk ad infinitum? Has man really gotten so smart that he's become terminally stupid and planning his own obsolescence and demise? This has been covered in detail in science fiction, and yet here we are. Who needs musicians ... they are flawed, just get HAL, and sure as hell don't forget the applause.
This isn't a question of can it be done; this is a question of why in the hell would we do it. If mankind's crowning achievement is making himself obsolete, then why did we work so hard to "evolve", to become more "learned", more "competent"?