I'm aware of the status of this. It looks like it will take until gnome shell 3.6-3.8 for it to catch up with ezoom.
Currently it's keyboard only stepped magnification, it follows the mouse pointer but doesn't have the sloppy push that works so well with ezoom. There are some dconf settings for changing the way it follows the mouse (org.gnome.a11y.magnifier.mouse-tracking). It is far worse than ezoom and limits the accessibility of gnome shell and cinnamon.
Ezoom is supposed to be finally getting text caret support - following the cursor as text is typed so you don't type off the screen. It's been promised since about 2004, whether gnome shell will gain that or not by 3.8 I'm not sure. In theory the wm just needs to know where the cursor is and whether the keyboard is being used without getting into the at-spi side of things.
It's cool, in many ways that with compiz, linux has had better magnification than OS-X and Windows (though there are commercial windows packages that exceed Compiz' abilities).