Special goods catered to specific subreddits.

On /r/fishing you obviously sell fishing supplies. On /r/$political_faction you sell bumper stickers with slogans. /r/nonbinary you sell pronoun pins.

It would be like an etsy or a shopify store for each subreddit with a UI that reflects that. It could also be a big Amazon style UI for a sitewide shop.

Like craigslist 2.0? They could capitalize on the fact that there are existing sub-communities around various niches.

Moderator privileges and astroturfing opportunities.

Karma and insults ?