Gnome developers are working hard to make the Gnome desktop and apps as simple, lightweight and fast as possible. One of the features that may make the apps and desktop simpler to use is the new kind of menus which are currently undergoing modifications.
Like the newer version of Google Chrome and Firefox, these apps will feature just one pull down menu from which other features of the apps can be accessed. This feature has already been developed implemented in Gnome 3.6, and hopefully will evolve further with the upcoming releases.
Mega Menus are being worked out, and some screenshots have been posted in Gnome Live page. The UI for the Gnome Image Viewer looks like this with Menu Buttons (can be invoked from bottom)
Here is what it will look like with Mega Menus
Here is what Mega Menus for Epiphany look like:
The Gnome teams are clearly focussing only on touch-based devices and distancing it from the traditional mouse/keyboard model. Mega Menus also mean it can't have a lot of sub-menu trees which would mean a lot of features and functionalities will be lost as you can't list everything in a single menu.
Please keep in mind that this is mid-development phase so many things may change in future.