Well, really I just haven't had the time to dig into it.  The code and approach is a lot different.  I need to tear it apart at some point because the author is entirely correct about the root cause of performance issues, but I haven't done that.  Back when @danielsdeleo steered me towards solving the problem of "how to get yajl 2.x into ruby" the Oj gem just wasn't on anyone's radar.