This repository and the GitHub pages deployment associated with it contain a proof-of-concept for a new double-sidebar for StudioCMS, proposed here.
Something that could be huge for UX is if we tied this behaviour to some sort of query param, so that the user can use the gestures of their mobile devide to head back. Since this navbar somewhat emulates the behaviour of mobile apps, it might be confusing for users, so we should give them the option. It is not difficult to implement, just not part of this POC (yet).