A register of proposals does seem like it would help to keep scientists honest, a step towards Feynman's "utter honesty." I would hesitate to say that journals should accept papers based solely on that register, though. Sometimes, the proposal might not end up as a wholly accurate description of the actual experiment, for a variety of reasons. I think that making both available would be a good way to judge how well the result actually applies to what is claimed by the scientists who published it. They could offer explanations for any differences between the proposal and the actual, and peer reviewers could give more thorough critiques with this extra information.