It would be possible to have something like that, but you'd have to code it yourself in an Embed Code element and it wouldn't be automatically updated. I could see that being a tidier way of including blog categories, though, if you've got a large number of them.
I do have a big catagory and its only going to get bigger as the site developes. Is there no way of Weebly intoducing this?
We could build something like that, although I wouldn't be able to say when or if that would happen. If you'd like us to do that feel free to post it to our Vote on Features board.