All I can say is this. I am 6'2" 280lbs. I fit on Space Mountain snug (but you know how much tighter that space is) and I never had any problem with Splash Mountain at all. Now with the lap bars it probably won't change a lot in my opinion and Disney is usually very good at making rides accomodating to bigger people so I am sure it was thought through very well.
I had to laugh though, typical of society huh? People are so dumb that they'll actually exit the ride and this is now something that will prevent morons from standing up or walking out. So now a lap bar has to be added based on the stupidity of the world. But we're getting smarter and progressing as humans right..........:lookaroun