As long as SP remains an easily used vector for Sybil attacks, I expect the adoption of SMT to be limited, as SMT could be as easily compromised by a Sybil attack on Steem blockchain as Steem itself.
I have noted that the churn rate on Steemit is far higher than other social media. The retention of users from 2016 is ~11%. I am pretty sure this is due to how SP is able to centralize control not only of witnesses (which most folks are unaware of) but also rewards.
When Steemit secures the blockchain against Sybil attacks, this may prove to be a game changer. If Steemit doesn't fix the problem (which is also a golden parachute for those that initially mined Steem, before Steemit even existed) the SEC might. Since SP weights votes that determine rewards and witnesses, Steem is definable as a security, like any other voting share stockholders may be familiar with, and the SEC is proceeding to regulate ICOs.
Time will tell.