I think it's a good idea, since the categories somewhat define "what's okay to talk about" (regardless of intent). I can see someone wanting to ask a non-tidyverse teaching question feeling that they shouldn't post here -- "uncategorized" feels dirty, somehow.
If it's added, it might be worth a small update to the pinned tidyverse category post pointing out that threads aimed primarily at teaching the tidyverse should go in the teaching category.