I don’t think it can be the case that we can’t make changes between rc1 and final — the whole point of the pre-release phase is to reveal these kind of issues.
I don’t like a transitional setting very much, but we’ve done similar a number of times in order to avoid a breaking change. I think we have to stick to the API stability policy, even in cases where we might be tempted to skip it.
I’d lean that way rather than revert, since this is a good change — we should keep it.