The Inline Entity Form provides a widget for reference fields that allows inline management (add / edit / delete) of referenced entities. It provides an excellent solution to the product display -> product UI problems, allowing the products (called "variations" in the UI) to be managed from the product display add / edit page.

The module also provides a more modern line item management widget, that allows store owners to edit custom fields that are attached to those line items.

Requires integration code to be provided for each entity type that can be referenced. Supports the node, commerce_product (including Commerce AutoSKU integration) and commerce_line_item entity types out of the box. Integration for other entity types has not yet been written, patches welcome.