This is an encouraging step in the right direction, thanks team!
However am I missing something or does the full-screen not give you any actual additional horizontal space within the layout? all the columns widths are preserved and I just get wide white margins on each side. Maybe it would have been better to call it focus mode 
?
Also, it doesn’t really play nice with Details Display which has its own full screen mode that preserves the navigation panel. I get that the new feature only affects the layout within the Details display, but this may not be obvious to all users.
Fullscreen is certainly nice, but 
all I want for Christmas is 
… in-canvas adjustable-width Details Display with conditional formatting and input validation! (and yes, I’m a greedy kid)