Yep that could be a problem if you have a lot of categories.
I think that the way that Discourse handles it with a dropdown is okay.
But if you wanted to go with the esotalk way with all the categories in the breadcrumb div, I think you could just have a control (like an arrow or even the word 'more') that would indicate there are more categories in the list. And clicking that would cause them to slide out or drop down.
But the bottom line is it would be nice to be able to quickly change/discover categories without having to go back to the Home page.