I'm backing sportstalk as it has the most potential to me for mass adoption and interaction. We are starting some fantasy leagues and competitions now which are fun and interactive.
What we will need are more tools for onboarding and ease of use for the blockchain. Then I can start to bring in friends to the site that never would be interested in steemit. But they do love sport and fantasy sports. I know hundreds who would love to compete and write about their teams and strategies for people to talk about. If they can earn some steem and buy sports equipment from it, even better.
Post all season and earn enough to buy the new jersey, a nice cap, tickets to the games. That would be the dream for a lot of sports fans. Hopefully we will get a steem connected debit card at some stage but that shouldn't be too far into the future going by other developments.