Full disclosure, I've never played go in real life. In fact only a handful of times on the family computer back in the early 90's (i486). Back then I had 0 understanding about the complexity of the game but now I can appreciate it.
Now, going away from this and into the following statement:
> said his retirement was primarily motivated by the invincibility of AI Go programs
I have a slight problem with that line of thoughts. Yes, there is undoubtedly a program that is thrashing humans left and right day in and day out. But I don't see why that would motivate someone to quit/retire. AI, in this day and age, to me at least, is still basically curve fitting. The fact that humans have figured out to do that in N-dimensional spaces (even with very large values of N), does not in any way undermine someone's effort and time dedicated to learning how to do a task. I'm sure that in several years someone will build an "AI" that can drive a modern Formula 1 car and it will smash all records and the best drivers without any efforts. And when that happens, should we abolish motorsports? Or sports in general? As humans we are confined to the limits of our biological abilities and personally I'm fine with that. I don't know who the first trillionaire will be, but I'm willing to bet that someone who figures out a way to interact with those models efficiently has a good chance. Essentially build a fast, all-accessible interface between the biological and digital world, which doesn't involve the traditional digital inputs(keyboard, screen, mouse, etc), and you have access to a decision making superpower at your disposal 24/7. When (and if) that happens, this is where games will cease to have any point. That's when it will boil down to who has the best hardware and software running along them rather than who is the best. Until then - game on!