There are still a bunch of jobs where machines are unlikely to replace humans anytime soon or ever, because the cost of deploying machines everywhere and maintaining them will also reach a plateau. We may be good soon at making brains for machine but they still need mechanical parts and require maintenance. So they have a non negligible cost.
But what if for almost every human supplied product/service there's a good enough machine substitue, or even just a human substitue that demands very little labor ? couldn't we reach a stable state of high unemployment ?