The point with that was to enable the transformers added through the config by default.  Alternative is to 
- force the user to do something like this in the config
    Exporter.Transformers = ['IPython.nbconvert.transformers.convertsvg.ConvertSvgTransformer']
    ConvertSvgTransformer.enabled = True
- or set enabled to True by default for all transformers

Open for suggestions