"SF don't inspire hope anymore" does not imply "SF has collapsed as a literary genre"; I'm not aware of "inspiring hope" being a factor in judging the existence of a literary genre.
However, I think a relevant data point in favor of Thiel's claim is this: where is our 2001: A Space Odyssey? That is, a work of hard-core sci-fi (10 on the "Mohs scale" of sci-fi) that's achieved mainstream success and entered the broader culture.
I cannot see how can anyone see 2001 as "inspiring hope".
Set in crapsack world of overpopulation, famine and imminent nuclear war, where human race was from the beginning a toy of omnipotent aliens. What hope? Our world in 2001 was not like in "2001", it was much better.
SIAI benefactor and VC Peter Thiel has an excellent article at National Review about the stagnating progress of science and technology, which he attributes to poorly-grounded political opposition, widespread scientific illiteracy, and overspecialized, insular scientific fields. He warns that this stagnation will undermine the growth that past policies have relied on.
Noteworthy excerpts (bold added by me):
In relation to concerns expressed here about evaluating scientific field soundness:
Grave indictors:
HT: MarginalRevolution