It would be interesting to see a broader analysis across subjects and see if that shared movement wasn't about AI and crypto, but largely just sort of a fluctuation in general tone across HN, or if instead relative to general HN sentiment, sentiment on Crypto an AI movements were correlated prior to the recent divergence.
*EDIT*
added an addendum to the post with the sentiment analysis graph including both rust and remote work.
Interestingly, there is in fact a noticeable downward slope in average sentiment over time for those topics as well, although they both remain far more popular than either AI or crypto.