Yes, sidebar was removed in 2.0/3.0.
Popover still works, but sidebar and menubar were removed.
With objc, we do now have a lot more flexibility, and can basically hack the interface in new ways.
i created a simple replacement for sidebar:
https://forum.omz-software.com/topic/3543/share-in-work-side-bar-replacement
Also, my matplotlib backend has a "shield free" floating window class, which can live in the editor, console, or root.
https://forum.omz-software.com/topic/3379/share-interactive-matplotlib-backend
Or, you can add buttons to the pythonista menu directly:
https://github.com/jsbain/objc_hacks/blob/master/apphack.py