It's pretty crucial that the base model and rigging be symmetrical, for content creation and proper functionality in the software.  Of course you know that. 

The asymmetrical morphs can be a final measure. Whatever morphs you create just give them each their split L & R counterparts, if it's a morph that would benefit from it. Not just the face but the body as well. But make them injectable. A figure with too many morphs pre-loaded in will bog down on a lot of people.