one Oracle should not have the absolute power to qualify or disqualify an account for rewards

So as I understand it, and I'm not totally up to speed on SMTs yet, this will be up to the SMT designer. I think It's entirely reasonable for one oracle to be used for some SMTs; if I want to make an SMT for people who post about curling, and I'm the only oracle for determining who posts about curling, that's probably fine. (Does anyone post about curling?)

The big high-concept SMTs with goals for changing the whole ecosystem will have to have more careful design to them. Probably only one or two of those will ever be at all effective, so in some sense the community will have a choice to go for the best-designed one. Whether we make that choice well....