Given that Steemit is still in beta, limited adoption is SOP.

Retention is a real problem, however, as only about ~11% of accounts created in 2016 remain active today.

There are reasons for that churn rate, and creating SMT not only doesn't address them, it may simply advertise them. This would not be good for Steemit in the long term, if it doesn't solve the retention problem. Successful media sites will have to consider the flaws in Steem, and how witnesses are vulnerable to Sybil attacks, before they can be counted on to adopt SMT in droves.