Sorry, I don't understand how this relates to fullscreen. I think fullscreen should by default only expand the editor widget like you want, but the GtkVPane widget we use doesn't have an easy way to do this AFAICT.
Lets say I had a keybinding for each of the following: 1. show message window 2. Show toolbar 3. show side panel
Then i could have a third key binding Full Screen: which would call 1, 2, 3, above