Keyboard shortcut for Zoom style?
I've written an AppleScript script which toggles the Zoom style:

tell application "System Events" to tell process "System Preferences"
    activate
    tell application "System Preferences"
        set the current pane to pane id "com.apple.preference.universalaccess"
        reveal anchor "Seeing_Zoom" of pane id "com.apple.preference.universalaccess"
    end tell
    delay 0.5
    tell pop up button "Zoom Style:" of window "Accessibility"
        click
        if value is equal to "Fullscreen" then
            pick menu item "Picture-in-picture" of menu 1
        else
            pick menu item "Fullscreen" of menu 1
        end if
    end tell
    tell application "System Preferences" to quit
end tell


You can use Keyboard Maestro or any other script launching app to run this script on a keyboard shortcut.