That's a good question. You cannot get a non-statistical guarantee of an output rate from the Von Neumann biased coin toss, because you can potentially get a long run of the same toss result, which stalls output bit generation. That might be a generic limitation of all similar de-biasing approaches. Has that been proven or disproven?
See my sibling reply [0]: for many input distributions, you can never put a fixed upper bound on the number of inputs you need to get a single output bit.
