In the Bayesian view, you can never really make absolute positive statements about truth anyway. Without a simplicity prior you would need some other kind of distribution. Even for computable theories, I don't think you can ever have a uniform distribution over possible explanations (math people, feel free to correct me on this if I'm wrong!); you could have some kind of perverse non-uniform but non-simplicity-based distribution, I suppose, but I would bet some money that it would perform very badly.