Maybe I'm missing something but Reddit/Imgur is essentially this generation's Usenet. Groups for anything imaginable, bigotry/flaming/trolling, lots of adult material. All that was missing from Usenet was a points system and descriptive groups directory.
Make a CMS with a points system on top of Usenet (tied to message-ID) that is sponsored by embedded ads instead of requiring a paid subscription. Block binaries with the exception of say, images - that way you're avoiding the vast majority of pirated materials. The points system would be similar to Reddit so that posts are ordered by rank but can still be sorted by date/poster. Posts/threads/users/groups can be canned from the CMS side. Posts censored? Feel free to switch to a pure Usenet service but you'll lose your points system/community.
By starting out on Usenet you already have content to begin with. Recall that Reddit started with fake user accounts with some quality content to get the ball rolling.
On further reflection...this would basically be Reddit as it is now.