I would love to be able to move sub-props into their own collections. I use FBX models as the "sets" for my animations. Very often these sets contain things that I would like to manage via a collection. For example, a chair in the set my be imported as 5 or more separate sub-props. I want to be able to group them together so I can rotate the chair as a whole. This also means that when I import the FBX set, I need to be able to create collections within the top level "set" object.