I feel like Communities are actually even bigger than the "gateway drug" infrastructure; they are the one thing that lets discovery happen organically and naturally as long as they're coupled with a decent search engine. They channelize discussion, keeping like things associated, making it easier to find things that are interested in and ultimately keep users engaged with the community much longer than any of the other alternatives.
It's one of the things that Google+ has done better than anyone else and one of the reasons that Facebook Pages are one of the only things that Facebook has got right.
"Moderation" might not be the right mindset to bring to driving social network engagement. Moderation implies a deliberate squelching of other people's content – legitimately so. But we know that people feel better about engaging with a system that promotes things that they like more than they enjoy engaging with a system that demotes things that they're not interested in at that moment.
In that sense, one of the strongest words and ideas associated with Steemit right now is "curation." Curation implies that you are helping other people find good stuff. People want to help other people. Let people help each other by working alongside the system to classify things for better discovery and you'll get better, longer term user engagement.
(Anyone that hasn't poked around it Google+ long enough to get past the media narrative that it is a "failed social network" needs to invest that time. Seriously, the Community interface and management system is top-notch. It's the best part about the entire system. Users can create their own Communities, manage and moderate those Communities, and take personal responsibility for the results. Google gets the vast benefit of channelize and content that is inherently self similar. Total win.)