Actually, I believe the Osmo mounting ring WAS shaved but only the part of the ring that needs to rotate under the X5. If you look closely from 2:45 onwards, you can see the top of the mounting ring on the left side (in the video) is actually lower than the other parts of the mounting ring. And he did not update the X5 in the DJI Go App.. what he actually did was calibrate it. I can't verify if the X5 can actually be calibrated on the Osmo with the latest DJI Go App because I am not desperate enough (yet) to shave my Osmo mounting ring so I am waiting for DJI's "impending release" of the X5 to Osmo adapter. This guy is actually trying to tout this as the first available X5 gimbal for sale and for interested parties to contact them.
Edit: You can actually see it very clearly at 0:29 the back part of the Osmo mounting ring is indeed shaved lower to accommodate the X5.