What I originally pictured was a random topic finder...say you hit randomize, then you get 10 random topics, possibly discovering something new or interesting or a new account of interest. So, it would kinda be the opposite of the post finder picked from topics.
One other idea I've had for content discovery is:
I mostly use peakd, for example, where there are mainly two feeds, followers and communities. They do have a "favorites" section, but that looks like it is for favorite accounts, not favorite topics-which is where it could be more useful.
If I could just add my favorite topics, say "fishing" or "crafts," then I could go to my favorite topics feed and find people posting about my favorite topics, discovering more content on the chain, finding new people to follow. You can click on your favorite topics, but it is kinda clunky and not organized like a recent feed.
Because of the tagging system, I think it really makes sense for a front end to do this...then the others follow suit after seeing how great of a feature it would be!