What if every user was essentially a topic? If someone found another user that creates posts that are always interesting to them regardless of the topic, their username/profile could be added as a topic they follow. It doesn't seem like it would be a massive change in the code base (though I could be wrong) and it also leaves Cake essentially the same while adding the ability to follow specific people if anyone wants to. You wouldn't even need to add any new tabs or anything. Just append "user-topics" or whatever to the end of the Following Topics page.
While I understand the main objective (and I do like it) of making interests the focal point, sometimes people make posts outside of our normal interests that we might like to learn more about but wouldn't be motivated to without some sort of forced exposure, so to speak. If you aren't already following those topics you miss them and you might end up in kind of an echo chamber unless you go out of your way to seek out new topics.