BTW: I disagree that intelligence and imagination are separate. I think intelligence necessarily includes imagination, so AI would include artificial "imagination" too.
I'd like progress to continue rather than to stagnate; and since progress has historically continued, that seems the way to bet. Those pundits predicting stagnation have historically been wrong. However, I find it curious that Kurzweil does not address the availability of innovations/discoveries (and the difficulty in finding them), in contrast to the compelling case he makes for historical progress. Are potential discoveries infinite? Is their density uniform, or do they become less likely as you go along because they are limited in supply (the assumption of the article)?
How would one sensibly model the supply of potential discoveries, since it is intrinsically unknown? Perhaps a mathematical model of computation might help, of computable functions and Kolomogorov/Solomonoff program length to compute them. Using this model, the search space of functions increases exponentially with program length - but at what rate would the number of "interesting" computable functions increase? And with what density (with respect to the search space, i.e. how hard they are to find)?