No, you're right, this doesn't make sense.  This logic is just sitting here as a temporary reminder for myself...  It's not what @ellisonbg and @minrk wanted me to do with 'configurable' logic.  In the end this will be split into subclasses.  Similar to what you had originally with the '/profiles' directory, but instead of using the traitlet and config system, standard python inheritance.  *Note*, it may seem like this is a step back towards nbconvert1; however, this is not the case.  The config system will still allow the user to specify custom defaults for each export configuration through the traitlet config system and make use of the Jinja template engine.