While it's possible to link to an entry with $(l:category_id/entry_id), it would be also be nice to able to link to a top-level category page with $(l:category_id).

This is pretty old so I hope it's okay if I bump this issue, to let you know I have wanted this feature when I was working on my own guide book.

this was implemented

This issue is stale because it has been open for a while with no activity. Please bump if this is still an issue, or this ticket will be closed soon.