Thats not always the case. There are plenty of coasters where at times of an inversion where you feel your weight against the shoulder restraints. Banshee's last inversion is a big example of this. I can't recall if Hulk had moments like that or not, but I think the initial zero G roll it probably happens. I'm not sure how the launch will work exactly, but if, for some reason, it doesn't launch at full speed and it makes a slow pass through there, you will be hanging against whatever restraints they use. Seat belts can be loosened by the rider. Most everyone who enjoys airtime coasters, know that its not hard to get more space when they do their checks. And those clamshells are not that restricting even when tight. With ride-ops having to do thousands of checks a day, not every one is going out is going to be perfectly tight. If they are going to do a no shoulder restrain design, it will be significantly redesigned to take those risks out of it, but i'm still betting on the vests.