[Update was confused to what this was] Available now over at Jag35 is the D|Zoom, which is a 'Zoom Lever' to control the 'Zoom Ring' on telephoto lenses.. To be used as in addition to a follow focus system (Prime lenses need not be concerned).

Pull the lever and it turns the zoom ring using the same lens gears as any mainstream follow focus. Keep in mind you'll still need a rail system and standard lens gears to operate.

D|Zoom Follow Focus