The possibility that there is no such thing as computationally tractable general intelligence (including in humans), just a bundle of hacks that work well enough for a given context.
Nobody said it has to work in every context. AGI just means something about as versatile as humans.
If Strong AI turns out to not be possible, what are our best expectations today as to why?
I'm thinking of trying myself at writing a sci-fi story, do you think exploring this idea has positive utility? I'm not sure myself: it looks like the idea that intelligence explosion is a possibility could use more public exposure, as it is.
I wanted to include a popular meme image macro here, but decided against it. I can't help it: every time I think "what if", I think of this guy.