Stepping back, I think it’s worth considering this in the context of “channel discovery” as a whole.
There are many things we can do to aid in making channels more discoverable. At the top of my list currently would be the ability to quickly mention another channel (“oh yeah, we were just discussing this in #community the other day”).
There are plenty of other things that could be done though… (Show related channels… have inbound links to posts when they are linked to from a channel… have discobot direct message you occasionally with channels you might want to join… post “channel created” messages to a “general” channel… have a tab for channels in topic lists…) You get the idea. Lots of possibilities.
Not sure exactly where we’ll start here, but if it’s helpful context for brainstorming, I’ll confirm that we are planning to remove the “per topic” channel feature, though you can have more than one channel in a category.