What hasn't been discussed is just how physically dangerous it would be to crash while pulling 6.7g. Guy would weigh the best part of half a ton when he hit the wall and would break every bone in his body if he tumbled.
My guess is that he has reached the limit for human endurance and to break the record you would need a much bigger, larger diameter wall. I am amazed he was able to keep control of the bike with that amount of pressure on his body. Like having a pallet of bricks on your back...