sparkcom
sparkcom
You may consider dependable dropdown such as http://plugins.krajee.com/dependent-dropdown/demo
The latter approach to inherit permissions from parent Product is logical. There is the same issue with Attribute and AttributeValue. PermissionProvider may be a good solution for them.
I make it SS4.2 compatible here https://github.com/sparkcom/silverstripe-blocks/tree/ss42-compatible I can maintain this module if that's ok.
i was looking at webfox/silverstripe-dropzone-sortable module but it's only SS3 . i hope there is a sortable feature for it