I think it is easier than it may seem looking at reddit. For example, for most, there will be enough something like curated categories. Let's say these categories can be created by users only from the Curators group. The same users will be moderators in the category they created.
Customization group. It is quite enough to display a custom banner of the curated category below the top menu and a widget of something like "similar posts from this category". Later, with the help of plugins, it is possible to give curators the opportunity to change several styles / colors of the main template for their category (of course, if someone needs this functionality).
So, we get 90% of the functionality of the reddit + what NodeBB itself brings. This can give a huge boost to some types of community that could grow at the expense of narrower niches covered by users.