@JasonT Thanks for bringing this up - because I'm in exactly the same situation. The Cake platform, the idea as well as the people behind it, everything is great but it's hard to just jump in and start posting if there's no real community for that specific topic yet.
"Post and they will come" is the general suggestion here - but "They aren't here yet, so I won't post" is something like a logical equivalent to that, and probably the more likely pick of the two for most people.
This is especially true for topics where I want to participate in, but wouldn't consider myself to be a real expert. I'd love to talk about anything ranging from Hiking, over that free-to-play online card game I currently enjoy, to Android development. I'd love to participate in discussions about woodworking, gardening or the next expansion for the Civilization VI video game - but being an "Average Joe" instead of someone who knows every nook and cranny regarding some of those topics, I'm hesitant to start a discussion when I don't know what discussion might come up (if any at all).
You brought up Reddit as a place where discussion already happens - and in fact, I lurk on Reddit for some of these topics, but would love to get away from it because it is often a vile place with all the anonymous downvoting and general trolling going on. Bootstrapping this is hard, though, so I'd appreciate any suggestions that might still come up here. :)