I poked around at a few of the other forums out there running discourse and something struck me - it wasn't clear what the forums were about. This 'meta' forum solves the problem with the pinned Welcome topic.
While looking around at other forums, its clear that this isn't universally done, though.
It feels like having some short about section that states what the forum is about would make sense.
Other forums help solve this by including excerpts of the posts or descriptions of the categories on the main page. But I have seen in other posts that this was experimented with here on Discourse before being deemed to be too much clutter (which I agree with).
On the Categories page, something similar may be appropriate. Currently, the description is shown when the mouse hover's over the label, but I know there is a desire to make everything work without hovers since tablets are a first class citizen.
So I think a simple 'what is this forum about' line above the list of topics could be a good way to address this in all cases. I've attached a mockup of what the meta.discourse.org FAQ category page may look like after doing this.
Or perhaps the description line belongs above the row of Filter tabs and Create button...