I think it would be beneficial to PlayFab and developers to be able to include the CollectionId on an InventoryOperation in order to save on calls made to the SDK / API. Instead of making a call per collection to add / subtract / update, each operation could be assigned a collection and all related operations on a single player's inventory could be done at once.
Having the collectionId on the same level as the Entity limits us to one call to add / subtract / update as many items as we want from a single collection and forces us to make a lot of calls if there are frequent updates to multiple different inventory collections.
Thanks.