If that's your definition of belief then it may not be that relevant. If I there's a game where someone roles a pair of fair six-sided dice and will give me five dollars if I can guess their sum, my best strategy is to guess 7 even though I don't by your definition believe that 7 will turn up. In this context this becomes a less than helfpul notation.

Also, if this is what you meant, I'm a bit confused by why you brought it up. Many prominent cryonics proponents give estimates well below 90%. So what point were you trying to make?