Let's take a look at some of the mockups available so far.
Simple Menu Button
A compact menu would be displayed on the window titlebar - for unmaximized windows only - and would show up when hovering the menu icon:
When the window is maximized, a Global Menu would show up on the top panel:
This menu would also have an option to turn it off for those who prefer traditional menus:
This is not a replacement for the regular window menu but for the right click menu:
For more info regarding each mockup, see https://live.gnome.org/Design/Whiteboards/Menus.
Please note that these are just ideas for now. There is no decision on what menus GNOME will use or even if the menus will be changed at all.
What do you think?
Thanks to zulu for the tip!