The state for UnfoldSequence doesn’t need the Bool in the first position in the tuple.
You can verify yourself that once you return nil (or .none as you do), the branches that check for $0.0 being true will never be called. It’s just dead code.
If you want I can go over the proposal before you make it official. It might also be good to add benchmarks to verify the rewritten version performs on par with current implementation.