One thing I've thought of on this topic is flatly contradictory to the workshop title: don't think of 'number of responses' or 'engagement' as a score in a game. For one thing, we're on Cake to have conversations, not to score points!
But more importantly still, Cake is the place where we talk about the things that interest us, not the things that we think will get most 'eyeballs'. Lidja touched on this above: genuine interest is the lifeblood of Cake. Some interests are fringe interests. If I make a fountain pen post, it will get fewer replies than someone's photography post, and that's fine! As Lidja said in her point 4, a discussion can be picked up months later, whether it's a current user finding it or a new user who joined just to talk about that topic.
It's not about the number of replies or reactions, after all -- it's about the great conversations we have :)