Well what will make steemit successful is the large adoption of users over time. In my opinion what will keep those users coming back is the casino like mechanism that is the payout schedule. It's not good/bad/indifferent that this is apart of the system. In reality all social media website have it - however with steemit the payout is actual cash vs. say likes & shares on Facebook. Even Facebook has this addicting quality to it where people are addicted to posting a picture of their dinner or Saturday night outfit and want to see how many people like/comment/share.

I think at this point in time it would be hard to argue against the fact a lot of people are here, using the site because of the payout system.