Your first point cannot be debated, since we are speculating. In practice, I'vent seen a problem. It works, it's clean, and it is the right amount of engineering needed to solve the problem.

Parse and Firebase example:

  //someservice.js
  ...
  //works as long as both retain the same interface.
  provider = new FirebaseProvider; //new ParseProvider()

  //add: just using an if condition, the old fashioned way.
  getProvider: function() {
    if (config.provider === 'parse')
      return ParseProvider()
    else
      return FirebaseProvider()
  

Why is writing configuration cleaner than doing the above? That thought process is carried over from projects with lengthy build time.