This would be great. It would fix #971484: Using Rules to reference the newly created product in a product_reference field as it is possible to populate the product entity - entity reference (node) field with the NID via a rule upon the creation of a product display node, but there is currently no way to populate the product reference field (aka sku) on the product display node - product reference field. Forcing the 2 entity reference fields to correspond would fix this! (Entity)Reference Field Synchronization should provide an api for custom entities to become synchronized. Product References would be a valuable start. Long-term all types of entities, limited or not, should be able to relate to each other in a 2-way relationship that can be triggered from either direction. Thanks