Thanks in part to Noel and PC for spotting this. I visited the stations at Hackney Central and Downs last night and spoke with staff. The new link is due to open in the summer and will provide a direct walkway from Platform 1 at Hackney Downs to Platform 2 at Hackney Central. There will be a pink validator along the walkway so that people avoiding zone 1 can indicate this. It would not surprise me if the OSI was removed once the walkway opens as it will be a considerably quicker route even if you have to change platforms within both stations. I do wonder whether the platforms at Central might need to be renumbered 5 and 6 to avoid confusion.