Besides if flex ever did get popular in corporate, which it's not...I just can't see some GV burning up 8000 ft of runway at 50% power, billionare in the back, white knuckles watching the plane lift off at the fence...
I don't think that's legal. Sure isn't on the aircraft I operate. 8% N1 reduction is the limit. In addition to that limit is my own. I always leave myself at least a 1000kg margin. My aircraft is not new and neither am I.