It could be simplified to its core. Picture New Twitter now but even simpler, and flipped horizontally. Post/item on the left side, and then banter on the right. Maybe one of the crew posts a jacket they're thinking of buying, or the result of a game, or a new movie trailer. Chit-chat fills the right hand side until people lose interest and move on to other posts.
Editing to add: I run a basketball forum which is a free-for-all. Anonymous posting, etc. And I often wonder how my experience of it would change if I just locked it down to the best 12-20 contributors - might miss a few challenging viewpoints, but there'd be no spam, griefers, brainless posts, etc. Perhaps picture the aforementioned concept as a micro-forum based around a particular niche rather than necessarily a particular group of friends?
And again (still thinking): You pick niches of interest and are randomly lumped with 12-20 others for as long as the group lasts. As with online gaming, you can privately kick out griefers or passengers. Perhaps you can only commit to 3 groups (wine, NBA, travel) to ensure you don't spread too thin. Elevator spiel is: Chatroulette + microforum + group decisions.