It would be helpful to edit/view two compositions inside of the same project simultaneously.
This could either happen by allowing multiple project browsers (that you already have) to go into the same project at once, and lock the project browser on the composition level instead. Or it could just be an added view, like in a code editor, that lives inside of one project browser. The latter would be more convenient, but I imagine the first option might be an easier MVP. Guess it depends on your data model.
This would be particularly helpful when copying excerpts from a transcript, or just referencing a transcript, while drafting a script.