It could work a bit like the quote: expanding upon clicking 
, so that the first paragraph would always be there as a reminder, and useful category links would be available right away on demand.
Once the category description is unpinned, and there are lots of topics, it’s hard to find if you don’t know the in:pinned search option.
I have another similar idea for Topics: the first post could be accessible from anywhere in the topic, which would make it more potent as a consolidation tool (and to comment on published pages)… But I’m getting ahead of myself.