subreddits are fantastic for that type of thing, and i like the ease of use and PRAW, however, handing over all of the community's data to conde nast isn't something i'm interested in.
what i'd like is a tool with which to create online communities, which would consist of a message board with upvotes/downvotes, user profiles, and perhaps a small chat system, with good mobile integration. as you said, it should be decentralized. it should also be as secure as possible without requiring non-standard software like TOR.