I like the idea, but honestly; do we really need one? The Revolution controller by itself is more than capable enough of performing the exact same functions. Sure, it's not shaped like a real gun, but try picking up your TV remote and aiming it around. It would work perfectly with no handle/trigger attachments; even more so with your fingers fitting perfectably into the grooves of the remote.
Damn, now I want to play Metroid Prime 3.