@akulbe: Just have a look at the number of features requested for SM itself, after it got out a few weeks ago. They can just be added one after another. There have been a couple of - I think - more important features to think about, like submodule support, worktrees, gitflow, ... and improving general usability of SM itself, which are needed by a wide range of users to be able to replace their old git gui with SM without loosing any crucial feature.
I even saw complains about SM being able to read the syntax definitions installed in ST.
I am looking forward for a more seamless integration of both as well, but agree with @srbs it is not the most important thing.