Sorting Shopify collections by product metafields is now possible for merchants on Pro and Enterprise plans.
- Go to Attributes, and scroll down to "Custom Attributes"
- Add a Custom Attribute, and select Metafields from the drop down
- Select a namespace, key, condition, value, and save the attribute. Don't forget to activate it!
- Head over to the Metrics tab and add the attribute to any or all of your Metrics Sets.