Allow for featured image to be displayed by default in variant images core

product.liquid

{% assign featured_image = product.featured_image | default: product.featured_image %}

select-callback.js

//wrap switch image in function

$('.single-option-selector').change(function(){
  if (variant.featured_image) {
     var newImage = variant.featured_image;
     etc..
  }
});

//add this below new optionSelectors

{% if product.variants.size > 1 %}
{% for option in product.options %}
 $('.single-option-selector:eq({{ forloop.index0 }})')
 .filter(function() { return $(this).find('option').size() > 1  })
 .prepend('<option value="">Choose ' + {{ product.options[forloop.index0] | json }} + '</option>')
 .val('')
 //hide this next line or it will interfere with callback code above
 //.trigger('change');
 {% endfor %}
 {% endif %}

Super Hacky. Not recommended.