We’ve seen a 600 DO patents before, no lens yet.
PR shows us a patent for a 600 f/5.6 DO lens. (JPO 2010-145832)
We’ve seen patents for DO lenses before. There are 300mm, 400m and 600mm DO patents.
Take a peak at some of the other lens patents Canon has filed. There was even one for a Zoom fisheye, though it’s different than what actually reached market.