> To my knowledge, this is the first time that serious AI researchers have publicly espoused the view that human-level or superhuman AI is impossible

Well, there's your first problem. Serious AI researchers have been publicly calling bullshit on superhuman AI since at least 1987, when my old professor Terry Winograd wrote the following in Understanding Computers and Cognition (1):

"one cannot build machines that either exhibit or model intelligence behavior"

The idea that "no serious researchers are skeptical about AGI" is a total fantasy perpetuated by people who haven o idea what they are talking about.

1. https://www.amazon.com/Understanding-Computers-Cognition-Fou...

Understanding Computers and Cognition: A New Foundation for Design by Terry Winograd and Fernando Flores. Highly recommended if you're interested in how people interact with computers (and how computers interact with people, and how both interact with the world in general). http://www.amazon.com/Understanding-Computers-Cognition-Foun...