I know you're going to hate this suggestion, that it is difficult or impossible to implement, and it makes Citadel *closer* to what you're trying to get away from - but I think if it could happen - it would generate more traffic and encourage more repeat traffic.
First - the ability to "like" posts. I know... I know... but what happens with likes is it encourages lurkers to interact. They don't have to say anything, but they can go, "I agree with this post," or "I like what this post is saying," without going through making a whole post to say, "Yeah... what he said..."
Second, it encourages content producers to create more content. Often, if I get several likes on a post, I'll expand on my original post, and that creates a positive feedback loop where I post more. Often, that will get people who agree to speak up and elaborate on their read of my post, stimulating conversation. Or, people will see the post getting likes, disagree, and feel like they have to speak up their opposition to what I am saying. Either way - it encourages conversation.
The other would be a mobile app, or at least mobile sharing. The ability to take a photo, or something else saved on your mobile device, add a little note, and share it - without first sending it to a PC... this encourages repeat usage - it creates discussion.
I know we can easily do most of this now and that the way it is creates a natural barrier to entry that actually keeps the userbase higher quality and more technical.
But maybe if something like this could be switched on or off, depending on what kind of userbase the sysop wants?
Just throwing ideas out there. I have no actually coding ability outside Access VBA - so it is all just a big pipe dream for me.
