I think he is playing it smart. The more fringe/contrarian it is, the bigger the payoff if he turns out to be right. So far nothing of much use came out of QC, and if nothing will, then the hype pendulum swings back at some point, and he will win big. If not, his position will seem silly, but not much risk to his reputation, being skeptic of a new model is intellectually fine and even courageous if it goes against the mainstream. I see it as those who called out "replication crisis" in social sciences.

If quantum computing never becomes commercially useful, Kalai will still have been wrong, because his claim is that things that have already happened are impossible. Perhaps in that case he might find it useful in public discourse to have "quantum skeptic" cred, since there'll be a general sense that the "quantum skeptics" were right, but that wouldn't change the fact that he specifically was wrong.