This is what I had in mind as well. For now, the "All stories" link in the header menu points you to the unfiltered stream.

As for discoverability: I forgot to mention it, but I thought of introducing a "neighbor distance" for a tag, which would include tags that are "close" by defining an edge `(u,v)` for tags `u, v` when they are both present in a story/post.  The idea being that relevant tags end up together in posts, and you can do a DFS/BFS and stop at the given distance.