> pepper.js shows that Pepper is effectively equivalent to the functionality the Web APIs provide

From my reading of it, pepper.js can only support a subset of Pepper's complete capabilities. At a high level, it is missing:

    - threads
    - memory mapping
    - memory protection

There's also stuff like this in pepper.js that clearly demonstrates a lack of parity:

    // The Web Audio API currently does not allow user-specified sample rates.
    var supportedSampleRate = function() {
      return createAudioContext().sampleRate;
    }

Also pepper.js is filled with chunks of code like:

    var FileRef_GetFileSystemType = function() {
      throw "FileRef_GetFileSystemType not implemented";
    };

    var FileRef_GetName = function() {
      throw "FileRef_GetName not implemented";
    };

    var FileRef_GetPath = function() {
      throw "FileRef_GetPath not implemented";
    };

    var FileRef_GetParent = function() {
      throw "FileRef_GetParent not implemented";
    };

    var FileRef_MakeDirectory = function() {
      throw "FileRef_MakeDirectory not implemented";
    };

    var FileRef_Touch = function() {
      throw "FileRef_Touch not implemented";
    };

I don't know enough about these APIs to say whether this is just incomplete or whether these Pepper calls can't be reasonably implemented on Web APIs, but pepper.js seems far from a demonstration that Pepper is "effectively equivalent" to Web APIs.