thank you for the response and all the information!
Since you mentioned that the DualPaneSelection Component is internal, we have experienced the same issue, that a component is internal, but we would like to use it with only slight modifications, with others as well.
To name two more examples:
The DropDownSelection, which is also a Relationship component, we had to copy-paste it together with some other internal dependencies declared by it.
The DetachedRepeat is only customizable as a whole, so while you can replace all of it, if you want to only customize a certain aspect of it, f. ex. its event buttons, they are again hard-wired into it and internal. And not only the event buttons, but also its other dependencies, which makes copy-pasting it almost impossible. There is another Thread regarding the DetachedRepeat here Customize "Commit" Button on Detached Repeat.
Maybe it would be worthwhile to consider a discussion for the other internal components as well?